C++: August 2014

Saturday, 23 August 2014

Data Structure and Algorithm - Linked List: Container

In this blog I have implemented a reasonably useful C++ version of Linked List container. It provides some basic and useful API to add/remove/sort/reverse the Linked List.

As this implementation is to use all the functions implemented on Data Structure and Algorithm - Linked List: Common API and Data Structure and Algorithm - Linked List: Merge Sort. So the major difficulty is to maintain the two cached property "m_Tail" and "m_Size". And the purpose is to achieve the same/better performance than C API implementation in Data Structure and Algorithm - Linked List: Common API and Data Structure and Algorithm - Linked List: Merge Sort.

Just realize that C++11 has introduced a new STL container called std::forward_list which is an implementation of single-linked-list. More details please refer to forward_list on cppreference. Read through its APIs and it provides the same sort of utilities as this implementation.

// C++ Implementation

// ********************************************************************************

// LinkedListContainer.h

#ifndef LINKED_LIST_CONTAINER_H

#define LINKED_LIST_CONTAINER_H

#include "LinkedListAlgo.h"

#include "LinkedListElement.h"

#include "LinkedListSort.h"

template <typename T>

class LinkedListContainer

{

typedef LinkedListElement<T>* NodePtr;

typedef LinkedListElement<T> Node;

public:

LinkedListContainer()

{}

~LinkedListContainer()

{

DeleteList();

}

void PushBack(const T& data)

{

LL_PushBack(&m_Tail, data);

if (m_Head == nullptr) {

// empty list before push

m_Head = m_Tail;

}

else {

m_Tail = m_Tail->next;

}

++m_Size;

}

void PushFront(const T& data)

{

LL_PushFront(&m_Head, data);

if (m_Tail == nullptr) {

// empty list before push

m_Tail = m_Head;

}

++m_Size;

}

void PopBack()

{

if (m_Head == nullptr) {

return;

}

if (m_Head == m_Tail) {

// empty list after pop

delete m_Tail;

m_Head = nullptr;

m_Tail = nullptr;

}

else {

NodePtr temp = m_Head;

while (temp) {

if (temp->next == m_Tail) {

break;

}

temp = temp->next;

}

delete m_Tail;

m_Tail = temp;

m_Tail->next = nullptr;

}

--m_Size;

}

void PopFront()

{

if (m_Head == nullptr) {

return;

}

LL_PopFront(&m_Head);

if (m_Head == nullptr) {

// empty list after pop

m_Tail = nullptr;

}

--m_Size;

}

bool Insert(size_t pos, const T& data)

{

if (pos > m_Size) {

return false;

}

if (pos == 0) {

PushFront(data);

}

else if (pos == m_Size) {

PushBack(data);

}

else {

LL_Insert(&m_Head, pos, data);

++m_Size;

}

return true;

}

bool Insert(const NodePtr posPtr, const T& data)

{

if (m_Head == nullptr || posPtr == nullptr) {

return false;

}

if (!LL_Insert(&m_Head, posPtr, data)) {

return false;

}

++m_size;

return true;

}

bool Erase(const size_t pos)

{

if (m_Head == nullptr || pos >= m_Size) {

return false;

}

if (pos == 0) {

PopFront();

}

else if (pos == (m_Size - 1)) {

PopBack();

}

else {

// in this case no need to update m_Tail

if (!LL_Erase(&m_Head, pos)) {

return false;

}

--m_Size;

}

return true;

}

// after this functin, posPtr becomes invalid

bool Erase(const NodePtr posPtr)

{

if (posPtr == m_Head) {

PopFront();

}

else if (posPtr == m_Tail) {

PopBack();

}

else {

// in this case no need to update m_Tail

if (!LL_Erase(&m_Head, posPtr)) {

return fasle;

}

--m_Size;

}

return true;

}

ptrdiff_t Find(const T& data)

{

NodePtr temp = m_Head;

ptrdiff_t pos = 0;

while (temp) {

if (temp->data == data) {

return pos;

}

++pos;

temp = temp->next;

}

return -1;

}

void Reverse()

{

m_Tail = m_Head;

LL_Reverse(&m_Head);

}

size_t GetSize() const {

return m_Size;

}

void MergeSort()

{

LL_MergeSort(&m_Head);

// reset m_Tail

ResetTail();

}

* After this opertaion, &other will lose the ownership

void SortedMerge(LinkedListContainer<T>& other)

{

m_Size += other.m_Size;

if (m_Tail->data < other.m_Tail->data) {

m_Tail = other.m_Tail;

}

m_Head = LL_SortedMerge(m_Head, other.m_Head);

// "other" has to lose the ownership, otherwise

// may cuase double free

other.m_Head = nullptr;

other.m_Tail = nullptr;

other.m_Size = 0;

}

void SortedMerge_Recursive(LinkedListContainer<T>& other)

{

m_Size += other.m_Size;

// m_Tail points the largest element

if (m_Tail->data > other.m_Tail->data) {

m_Tail = other.m_Tail;

}

m_Head = LL_SortedMergeRecursively(m_Head, other.m_Head);

}

* Has to work on a sorted linkedlist

void RemoveDuplicates()

{

if (m_Head == nullptr){

return;

}

// Do not call LL_RemoveDuplicates()

// otherwise has to update m_Tail and m_Size

// cause worse performance

NodePtr curValPtr = m_Head;

NodePtr nextValPtr = m_Head->next;

while (nextValPtr != nullptr) {

if (nextValPtr->data == curValPtr->data) {

curValPtr->next = nextValPtr->next;

delete nextValPtr;

nextValPtr = curValPtr->next;

--m_Size;

}

else {

curValPtr = nextValPtr;

nextValPtr = nextValPtr->next;

}

m_Tail = curValPtr;

return;

}

void DeleteList()

{

LL_Delete(&m_Head);

// m_Head should set as nullptr already

m_Tail = nullptr;

m_Size = 0;

}

bool GetNth(size_t n, T& t)

{

return LL_GetNth(m_Head, n, t);

}

void Print(std::ostream& os)

{

NodePtr temp = m_Head;

while (temp != nullptr) {

os << temp->data;

temp = temp->next;

}

private:

void ResetTail()

{

NodePtr prev = m_Head;

m_Tail = m_Head;

while (m_Tail != nullptr) {

prev = m_Tail;

m_Tail = m_Tail->next;

}

m_Tail = prev;

}

NodePtr m_Head = nullptr;

NodePtr m_Tail = nullptr;

size_t m_Size = 0;

};

#endif

// test.cpp

void TestLinkedListContainer()

{

LinkedListContainer<int> myLLC;

myLLC.PushFront(10);

assert(myLLC.GetSize() == 1);

myLLC.PushBack(20);

assert(myLLC.GetSize() == 2);

int val;

assert(myLLC.GetNth(0, val) == true);

assert(val == 10);

assert(myLLC.GetNth(1, val) == true);

assert(val == 20);

myLLC.PushFront(30);

assert(myLLC.GetSize() == 3);

assert(myLLC.GetNth(0, val) == true);

assert(val == 30);

myLLC.PopFront();

assert(myLLC.GetSize() == 2);

assert(myLLC.GetNth(0, val) == true);

assert(val == 10);

myLLC.PopBack();

assert(myLLC.GetSize() == 1);

assert(myLLC.GetNth(0, val) == true);

assert(val == 10);

myLLC.PopFront();

assert(myLLC.GetSize() == 0);

assert(myLLC.GetNth(0, val) == false);

myLLC.PushBack(40);

assert(myLLC.GetSize() == 1);

assert(myLLC.GetNth(0, val) == true);

assert(val == 40);

myLLC.PushFront(50);

assert(myLLC.GetSize() == 2);

assert(myLLC.GetNth(0, val) == true);

assert(val == 50);

myLLC.PopFront();

assert(myLLC.GetNth(0, val) == true);

assert(val == 40);

myLLC.PopBack();

assert(myLLC.GetSize() == 0);

assert(myLLC.Insert(2, 30) == false);

assert(myLLC.GetSize() == 0);

assert(myLLC.Insert((size_t)0, 30) == true);

assert(myLLC.GetSize() == 1);

assert(myLLC.GetNth(0, val) == true);

assert(val == 30);

myLLC.PushBack(40);

assert(myLLC.GetSize() == 2);

assert(myLLC.GetNth(1, val) == true);

assert(val == 40);

myLLC.PopFront();

assert(myLLC.GetSize() == 0);

// construct 9, 12, 10, 3, 20, 18, 10, 40

myLLC.PushFront(3);

myLLC.PushFront(10);

myLLC.PushFront(12);

myLLC.PushFront(9);

myLLC.PushBack(20);

myLLC.PushBack(18);

myLLC.PushBack(10);

myLLC.PushBack(40);

assert(myLLC.GetSize() == 8);

assert(myLLC.GetNth(0, val) == true);

assert(val == 9);

assert(myLLC.GetNth(1, val) == true);

assert(val == 12);

assert(myLLC.GetNth(2, val) == true);

assert(val == 10);

assert(myLLC.GetNth(3, val) == true);

assert(val == 3);

assert(myLLC.GetNth(4, val) == true);

assert(val == 20);

assert(myLLC.GetNth(5, val) == true);

assert(val == 18);

assert(myLLC.GetNth(6, val) == true);

assert(val == 10);

assert(myLLC.GetNth(7, val) == true);

assert(val == 40);

assert(myLLC.GetNth(8, val) == false);

// construct 9, 12, 10, 3, 20, 18, 10, 40

// 3, 9, 10, 10, 12, 18,20, 40

myLLC.MergeSort();

assert(myLLC.GetSize() == 8);

assert(myLLC.GetNth(0, val) == true);

assert(val == 3);

assert(myLLC.GetNth(1, val) == true);

assert(val == 9);

assert(myLLC.GetNth(2, val) == true);

assert(val == 10);

assert(myLLC.GetNth(3, val) == true);

assert(val == 10);

assert(myLLC.GetNth(4, val) == true);

assert(val == 12);

assert(myLLC.GetNth(5, val) == true);

assert(val == 18);

assert(myLLC.GetNth(6, val) == true);

assert(val == 20);

assert(myLLC.GetNth(7, val) == true);

assert(val == 40);

assert(myLLC.GetNth(8, val) == false);

assert(myLLC.Erase(8) == false);

// 3, 9, 10, 10, 12, 18, 20

assert(myLLC.Erase(7) == true);

// 9, 10, 10, 12, 18, 20

assert(myLLC.Erase((size_t)0) == true);

// 9, 10, 10, 18, 20

assert(myLLC.Erase(3) == true);

assert(myLLC.GetSize() == 5);

assert(myLLC.GetNth(0, val) == true);

assert(val == 9);

assert(myLLC.GetNth(1, val) == true);

assert(val == 10);

assert(myLLC.GetNth(2, val) == true);

assert(val == 10);

assert(myLLC.GetNth(3, val) == true);

assert(val == 18);

assert(myLLC.GetNth(4, val) == true);

assert(val == 20);

assert(myLLC.GetNth(5, val) == false);

// 9, 10, 18, 20

myLLC.RemoveDuplicates();

assert(myLLC.GetSize() == 4);

assert(myLLC.GetNth(0, val) == true);

assert(val == 9);

assert(myLLC.GetNth(1, val) == true);

assert(val == 10);

assert(myLLC.GetNth(2, val) == true);

assert(val == 18);

assert(myLLC.GetNth(3, val) == true);

assert(val == 20);

assert(myLLC.GetNth(5, val) == false);

// 20, 9, 10, 18, 20

assert(myLLC.Insert((size_t)0, 20) == true);

// 20, 9, 10, 18, 9, 20

assert(myLLC.Insert(4, 9) == true);

// 20, 9, 10, 18, 9, 20, 18

assert(myLLC.Insert(6, 18));

assert(myLLC.GetSize() == 7);

assert(myLLC.GetNth(0, val) == true);

assert(val == 20);

assert(myLLC.GetNth(1, val) == true);

assert(val == 9);

assert(myLLC.GetNth(2, val) == true);

assert(val == 10);

assert(myLLC.GetNth(3, val) == true);

assert(val == 18);

assert(myLLC.GetNth(4, val) == true);

assert(val == 9);

assert(myLLC.GetNth(5, val) == true);

assert(val == 20);

assert(myLLC.GetNth(6, val) == true);

assert(val == 18);

assert(myLLC.GetNth(7, val) == false);

// 9, 9, 10, 18, 18, 20, 20

myLLC.MergeSort();

assert(myLLC.GetSize() == 7);

assert(myLLC.GetNth(0, val) == true);

assert(val == 9);

assert(myLLC.GetNth(1, val) == true);

assert(val == 9);

assert(myLLC.GetNth(2, val) == true);

assert(val == 10);

assert(myLLC.GetNth(3, val) == true);

assert(val == 18);

assert(myLLC.GetNth(4, val) == true);

assert(val == 18);

assert(myLLC.GetNth(5, val) == true);

assert(val == 20);

assert(myLLC.GetNth(6, val) == true);

assert(val == 20);

assert(myLLC.GetNth(7, val) == false);

// 9, 10, 18, 20

myLLC.RemoveDuplicates();

assert(myLLC.GetSize() == 4);

assert(myLLC.GetNth(0, val) == true);

assert(val == 9);

assert(myLLC.GetNth(1, val) == true);

assert(val == 10);

assert(myLLC.GetNth(2, val) == true);

assert(val == 18);

assert(myLLC.GetNth(3, val) == true);

assert(val == 20);

assert(myLLC.GetNth(4, val) == false);

// const another list 1, 15, 25, 19, 12

LinkedListContainer<int> myLLC2;

myLLC2.PushFront(25);

myLLC2.PushBack(19);

myLLC2.PushFront(15);

myLLC2.PushBack(12);

myLLC2.PushFront(1);

assert(myLLC2.GetSize() == 5);

// 1, 12, 15, 19, 25

myLLC2.MergeSort();

assert(myLLC2.GetSize() == 5);

assert(myLLC2.GetNth(0, val) == true);

assert(val == 1);

assert(myLLC2.GetNth(1, val) == true);

assert(val == 12);

assert(myLLC2.GetNth(2, val) == true);

assert(val == 15);

assert(myLLC2.GetNth(3, val) == true);

assert(val == 19);

assert(myLLC2.GetNth(4, val) == true);

assert(val == 25);

assert(myLLC2.GetNth(5, val) == false);

// 1, 9, 10, 12, 15, 18, 19, 20, 25

myLLC.SortedMerge(myLLC2);

assert(myLLC2.GetSize() == 0);

assert(myLLC.GetSize() == 9);

assert(myLLC.GetNth(0, val) == true);

assert(val == 1);

assert(myLLC.GetNth(1, val) == true);

assert(val == 9);

assert(myLLC.GetNth(2, val) == true);

assert(val == 10);

assert(myLLC.GetNth(3, val) == true);

assert(val == 12);

assert(myLLC.GetNth(4, val) == true);

assert(val == 15);

assert(myLLC.GetNth(5, val) == true);

assert(val == 18);

assert(myLLC.GetNth(6, val) == true);

assert(val == 19);

assert(myLLC.GetNth(7, val) == true);

assert(val == 20);

assert(myLLC.GetNth(8, val) == true);

assert(val == 25);

assert(myLLC.GetNth(9, val) == false);

}

//********************************************************************************

Side-talk of TDD:

In these 4 blogs for Linked List, I have really enjoyed and experienced the power of Test Driven Development (test implementation, production code implementation, regression testing, code refactoring and repeat the 4 steps. See TDD on wiki). Especially experience on the micro-cycle implementation of TDD. In my mind, TDD can be implemented in two different scopes, one (macro scope) is on the sprint/user-story scope and another (micro scope) is on the unit-test scope. I did enjoyed the TDD implementation on macro scope, because it is more about acceptance testing and serves a good indication against what the software is about to delivery. But I never enjoyed the micro scope because I thought is was too tedious and time-consuming. Time-consuming was always my excuse not to do so by arguing not having enough resource/time.

But in these four blogs I found the power and joy of micro implementation of TDD. One of good example is to decide passing a pointer to pointer "**" or a pointer "*" to LinkedListElement as the argument, as I mentioned this issue on Data Structure and Algorithm - Linked List: Common API. The same function, for instance "LL_PushFront", depends on the setup of the test. By passing a pointer "*" this function will work as expected, if the "head" is not empty/nullptr. But if it is an empty list ("head" is nullptr), then passing a pointer "*" to LinkedListElement will not work and it has to pass as a pointer to a pointer "**" to LinkedListElement because it is to change the value of "head" when the Linked List becomes from empty to non-empty. This kinds of design errors can be easily spotted by TDD in a very intuitive sense by adding tiny tests one by one. Otherwise it may take some seriously debugging. I have to say from now on I will adopt this idiom.

Bibliography:
[1] http://cslibrary.stanford.edu/105/LinkedListProblems.pdf
[2] Glenn W. Rowe, Data Structure & Algorithm C++, Prentice Hall, 1996
[3] http://en.wikipedia.org/wiki/Test-driven_development
[4] http://en.cppreference.com/w/cpp/container/forward_list

Sunday, 17 August 2014

Data Structure and Algorithm - Linked List: Circle Detection

This is one of interviewing questions that my friends and I all have encountered and used in quite a few occasions. And I believe it is worth of one blog.

1. Problem
Given the fact that in my last two blog entries, Data Structure and Algorithm - Linked List: Common API and Data Structure and Algorithm - Linked List: Merge Sort, these algorithms and implementation are only operational on Linked List without circle linking. Otherwise some of them will be lost in loop. For instance, LL_PushBack(), this operation will be trapped in the loop to find the last node, if a circle linking exists in the Linked List.

Hence it will be circular to guarantee that there does not exist circle linking in the Linked List when using these functions. Hence circle detection algorithm is useful for this occasion.The goal is to design/implement an algorithm to remove the circle linking if it does exist.

2. Solution 1 - Hash Table
This is the first intuitive solution popping into my head. It is similar to use a linear method to find the very first repeating number given an array. Use hash table to contain the hash value of the pointer in order to speed up the searching. It guarantees that traversing the Linked List once will find the solution. But one drawback of this solution is that its correctness depends on the quality of the hash function. Given a perfect hash function to guarantee different input producing different output, then this solution will work as expected.

// Pseudo-code
//********************************************************************************
curHead <- Current head of this Liked List
ptrHashTable <- Initialize this hash table
lastNodeOfCircle <- nullptr
while (curHead is not nullptr)
  hashVal <- Compute the hash value of curHead
if (hashVal does not exist in ptrHashTable)
  ptrHashTable <- Insert hashVal
  lastNodeOfCircle <- curHead
  curHead <- (curHead->next)
  else
  lastNodeOfCircle <- nullptr
Found and return
Not found and return
//********************************************************************************

3. Solution 2 - Two Speeds of Traversing
The basic idea behind of this solution is to use two pointers traversing the Linked List with two different speed. The slower pointer traverses one node by another and the faster pointer traverses twice faster than the slower. Think about the clock. Obviously three hands (second, minute and hour) go around and around the clock. Assuming at the moment of midnight three hands meet at the 12, (actually no matter any position these three hands are currently now), the second hand can always catch the minute and hour hands and the minute hand can always catch the hour hand. Because the second hand moves faster than other two and the minute hand moves faster than the hour hand. This algorithm uses the exactly the same idea - the faster can always catch the slower in a circle arena.

If the circle linking does exists, traverse the Linked List and the faster pointer will eventually catch the slower one. If does not exist, the faster pointer will reach the end of the Linked List first. In order to remove the circle linking, the key is to find the last node in the Linked List. In the clock example, if the head is set as "12", then the last node of the circle is "11". Removing the circle is simple - break the link and set the "next" of the last node in the circle as nullptr.

// C implementation
//********************************************************************************
// LinkedListCircleDetect.h
#ifndef LINKED_LIST_CIRCLE_DETECT_H
#define LINKED_LIST_CIRCLE_DETECT_H

#pragma once

#include "LinkedListElement.h"

template<typename T>
LinkedListElement<T>* LL_GetOneOfNodesInCircleIfExists(LinkedListElement<T>* head)
{
if (head == nullptr) {
return nullptr;
}

LinkedListElement<T>* slow = head;
LinkedListElement<T>* fast = head;

  while (1) {
for (int speed = 0; speed < 2; ++speed) {
fast = fast->next;
if (fast == nullptr) {
return nullptr;
}
if (slow == fast) {
return slow;
}
}

slow = slow->next;
}

return nullptr;
}

template<typename T>
bool LL_CheckIfCircleExists(LinkedListElement<T>* head)
{
return LL_GetOneOfNodesInCircleIfExists(head) != nullptr;
}

template<typename T>
size_t LL_GetCircleSizeIfExists(LinkedListElement<T>* head)
{
LinkedListElement<T>* oneNodeInCircle = LL_GetOneOfNodesInCircleIfExists(head);

if (oneNodeInCircle == nullptr) {
return 0;
}

size_t count = 1;
LinkedListElement<T>* cur = oneNodeInCircle->next;
while (cur != oneNodeInCircle) {
cur = cur->next;
++count;
}

return count;
}

template<typename T>
LinkedListElement<T>* LL_DetectTheLastNodeOfCircleIfExists(LinkedListElement<T>* head)
{
size_t circleSize = LL_GetCircleSizeIfExists(head);

if (circleSize == 0) {
return nullptr;
}

LinkedListElement<T>* cur = head;
LinkedListElement<T>* tempOffsetByCircleSize = head;

  while (--circleSize > 0) {
tempOffsetByCircleSize = tempOffsetByCircleSize->next;
}

while (cur != tempOffsetByCircleSize->next) {
cur = cur->next;
tempOffsetByCircleSize = tempOffsetByCircleSize->next;
}

return tempOffsetByCircleSize;
}

/*
* If circle does not exsit, return false
* If circle exists, then remove the circle and return true
*/
template<typename T>
bool LL_RemoveCircleIfExists(LinkedListElement<T>** head)
{
if (head == nullptr) {
return false;
}
LinkedListElement<T>* lastNodeOfCircle = LL_DetectTheLastNodeOfCircleIfExists(*head);
if (lastNodeOfCircle == nullptr) {
return false;
}

lastNodeOfCircle->next = nullptr;
return true;
}

#endif

// test.cxx

void TestLinkedListCircleDetector()

{

LinkedListElement<int>* head = nullptr;

// empty list

assert(LL_GetOneOfNodesInCircleIfExists(head) == nullptr);

assert(LL_CheckIfCircleExists(head) == false);

assert(LL_GetCircleSizeIfExists(head) == 0);

assert(LL_DetectTheLastNodeOfCircleIfExists(head) == nullptr);

assert(LL_RemoveCircleIfExists(&head) == false);

LL_PushFront(&head, 11);

LinkedListElement<int>* tail = head;

// point to itself

tail->next = head;

assert(LL_GetOneOfNodesInCircleIfExists(head) != nullptr);

assert(LL_CheckIfCircleExists(head) == true);

assert(LL_GetCircleSizeIfExists(head) == 1);

assert(LL_DetectTheLastNodeOfCircleIfExists(head) == tail);

assert(LL_RemoveCircleIfExists(&head) == true);

assert(head->next == nullptr);

assert(head->data == 11);

// construct 12, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11

LL_PushFront(&head, 10);

LL_PushFront(&head, 9);

LL_PushFront(&head, 8);

LL_PushFront(&head, 7);

LL_PushFront(&head, 6);

LL_PushFront(&head, 5);

LL_PushFront(&head, 4);

LL_PushFront(&head, 3);

LL_PushFront(&head, 2);

LL_PushFront(&head, 1);

LL_PushFront(&head, 12);

assert(LL_GetOneOfNodesInCircleIfExists(head) == nullptr);

assert(LL_CheckIfCircleExists(head) == false);

assert(LL_GetCircleSizeIfExists(head) == 0);

assert(LL_DetectTheLastNodeOfCircleIfExists(head) == nullptr);

assert(LL_RemoveCircleIfExists(&head) == false);

// setup the circle

tail->next = head;

assert(LL_GetOneOfNodesInCircleIfExists(head) != nullptr);

assert(LL_CheckIfCircleExists(head) == true);

assert(LL_GetCircleSizeIfExists(head) == 12);

assert(LL_DetectTheLastNodeOfCircleIfExists(head) == tail);

assert(LL_RemoveCircleIfExists(&head) == true);

assert(tail->next == nullptr);

assert(LL_GetSize(head) == 12);

int val;

assert(LL_GetNth(head, 12, val) == false);

// setup the circle

tail->next = head;

LL_PushFront(&head, 20);

LL_PushFront(&head, 30);

LL_PushFront(&head, 40);

LL_PushFront(&head, 50);

LL_PushFront(&head, 60);

LL_PushFront(&head, 70);

assert(LL_GetOneOfNodesInCircleIfExists(head) != nullptr);

assert(LL_CheckIfCircleExists(head) == true);

assert(LL_GetCircleSizeIfExists(head) == 12);

assert(LL_DetectTheLastNodeOfCircleIfExists(head) == tail);

assert(LL_RemoveCircleIfExists(&head) == true);

assert(tail->next == nullptr);

assert(LL_GetSize(head) == 18);

assert(LL_GetNth(head, 18, val) == false);

LL_Delete(&head);

}

//********************************************************************************

4. Summary
The first solution using hash table is to guarantee O(N) computation complexity and O(N) space complexity. The second solution is to guarantee O(N) computation complexity as well but only O(1) space complexity. But the second solution could run ~3 times slower than the first solution in the worst case, because it needs to traverse the Linked List to detect if the circle does exist, traverse again to find out the size of circle, and traverse the third time to find out the last node of the circle. And it is fair that the first solution trades space for speed.

Bibliography:
[1] http://cslibrary.stanford.edu/105/LinkedListProblems.pdf
[2] Glenn W. Rowe, Data Structure & Algorithm C++, Prentice Hall, 1996

Thursday, 14 August 2014

Data Structure and Algorithm - Linked List: Merge Sort

As I presented the common API for Linked List in my last blog entry, Data Structure and Algorithm - Linked List (Part I), in this blog I would like to present a sorting algorithm for Linked List, merge sort. Please refer to the basic idea about sorting in Data Structure and Algorithm - Sort and Binary Search.

Why Merge Sort
- Simply idea: divide and conquer
- Easy adapted to parallel computing
- Space complexity: O(1) for Linked List, comparing with other sorting algorithm
- Better performance than other more efficient algorithm in theory due to the traverse of Linked List
- Guarantee to be stable sort
- Guarantee to the worst case of O(N*logN)

// C implementation of Merge Sort on Linked List
//********************************************************************************
// LinkedListSort.h
#ifndef LINKED_LIST_SORT_H
#define LINKED_LIST_SORT_H

#pragma once

#include "LinkedListAlgo.h"
#include "LinkedListElement.h"

template<typename T>
void LL_MergeSort(LinkedListElement<T>** head)
{
if (head == nullptr || *head == nullptr || (*head)->next == nullptr) {
return;
}

LinkedListElement<T>* front = nullptr;
LinkedListElement<T>* back = nullptr;
LL_FrontBackSplit(*head, &front, &back);
LL_MergeSort(&front);
LL_MergeSort(&back);
*head = LL_SortedMerge(front, back);
}

template<typename T>
void LL_FrontBackSplit(LinkedListElement<T>* src,
LinkedListElement<T>** front,
LinkedListElement<T>** back)
{
if (src == nullptr) {
return;
}

LinkedListElement<T>* slow = src;
LinkedListElement<T>* fast = src->next;
while (fast != nullptr) {
fast = fast->next;
if (fast != nullptr) {
slow = slow->next;
fast = fast->next;
}
}

*front = src;
*back = slow->next;
slow->next = nullptr;
}

template<typename T>
LinkedListElement<T>* LL_SortedMerge(LinkedListElement<T>* l1,
LinkedListElement<T>* l2)
{
LinkedListElement<T> temp;
LinkedListElement<T>* cur = &temp;

while (l1 != nullptr || l2 != nullptr) {
if (l1 == nullptr) {
cur->next = l2;
return temp.next;
}
if (l2 == nullptr) {
cur->next = l1;
return temp.next;
}
if (l1->data <= l2->data) {
cur->next = l1;
cur = cur->next;
l1 = l1->next;
}
else {
cur->next = l2;
cur = cur->next;
l2 = l2->next;
}
}

return temp.next;
}

template<typename T>
LinkedListElement<T>* LL_SortedMergeRecursively(LinkedListElement<T>* l1,
LinkedListElement<T>* l2)
{
if (l1 == nullptr) {
return l2;
}
if (l2 == nullptr) {
return l1;
}

LinkedListElement<T>* result = nullptr;
if (l1->data <= l2->data) {
result = l1;
result->next = LL_SortedMergeRecursively(l1->next, l2);
}
else {
result = l2;
result->next = LL_SortedMergeRecursively(l1, l2->next);
}

return result;
}

template<typename T>
void LL_RemoveDuplicates(LinkedListElement<T>** head)
{
if (head == nullptr || *head == nullptr || (*head)->next == nullptr) {
return;
}

LinkedListElement<T>* curValPtr = *head;
LinkedListElement<T>* nextValPtr = (*head)->next;
while (nextValPtr != nullptr) {
if (nextValPtr->data == curValPtr->data) {
curValPtr->next = nextValPtr->next;
delete nextValPtr;
nextValPtr = curValPtr->next;
}
else {
curValPtr = nextValPtr;
nextValPtr = nextValPtr->next;
}
}

return;
}

/*
* create a new list which is intersection of two lists
* no duplicate in this list
* l1 and l2: has to be sorted linked list
*/
template<typename T>
LinkedListElement<T>* LL_SortedIntersect(LinkedListElement<T>* l1,
LinkedListElement<T>* l2)
{
if (l1 == nullptr || l2 == nullptr) {
return nullptr;
}

LinkedListElement<T>* head = nullptr;
ptrdiff_t found;
size_t pos = 0;
LinkedListElement<T>* curValPtr = nullptr;
while (l1 != nullptr) {
if (curValPtr == nullptr || curValPtr->data != l1->data) {
curValPtr = l1;

found = LL_Find(l2, pos, curValPtr->data);
if (found >= 0) {
LL_PushFront(&head, curValPtr->data);
pos = static_cast<size_t>(found + 1);
}
}
l1 = l1->next;
}

return head;
}

template<typename T>
bool LL_SortedInsert(LinkedListElement<T>** head, const T& val)
{
if (head == nullptr) {
return false;
}

if (*head == nullptr) {
LL_PushFront(head, val);
return true;
}

if (val <= (*head)->data) {
LL_PushFront(head, val);
return true;
}

LinkedListElement<T>* prev = *head;
LinkedListElement<T>* cur = (*head)->next;

while (cur != nullptr) {
if (cur->data >= val) {
prev->next = new LinkedListElement<T>(val);
prev->next->next = cur;
return true;
}
prev = cur;
cur = cur->next;
}

// hit here not found the position
// LL_PushBack(head, val);
prev->next = new LinkedListElement<T>(val);
return true;
}

#endif

// test.cpp

void TestLinkedListSort()

{

LinkedListElement<int>* head1 = nullptr;
// construct list: 10, 9, 20, 8, 7, 7, 20, 30, 50, 20, 4, 3,
LL_PushFront(&head1, 3);
LL_PushFront(&head1, 4);
LL_PushFront(&head1, 20);
LL_PushFront(&head1, 50);
LL_PushFront(&head1, 30);
LL_PushFront(&head1, 20);
LL_PushFront(&head1, 7);
LL_PushFront(&head1, 7);
LL_PushFront(&head1, 8);
LL_PushFront(&head1, 20);
LL_PushFront(&head1, 9);
LL_PushFront(&head1, 10);
assert(LL_GetSize(head1) == 12);

LinkedListElement<int>* head2 = nullptr;
// const list: 12, 17, 56, 19, 18, 10, 9, 12, 6, 8, 10
LL_PushFront(&head2, 10);
LL_PushFront(&head2, 8);
LL_PushFront(&head2, 6);
LL_PushFront(&head2, 12);
LL_PushFront(&head2, 9);
LL_PushFront(&head2, 10);
LL_PushFront(&head2, 18);
LL_PushFront(&head2, 19);
LL_PushFront(&head2, 56);
LL_PushFront(&head2, 17);
LL_PushFront(&head2, 12);
assert(LL_GetSize(head2) == 11);

LL_MergeSort(&head1); // 3, 4, 7, 7, 8, 9, 10, 20, 20, 20, 30, 50

int val;
assert(LL_GetNth(head1, 0, val) == true);
assert(val == 3);
assert(LL_GetNth(head1, 1, val) == true);
assert(val == 4);
assert(LL_GetNth(head1, 2, val) == true);
assert(val == 7);
assert(LL_GetNth(head1, 3, val) == true);
assert(val == 7);
assert(LL_GetNth(head1, 4, val) == true);
assert(val == 8);
assert(LL_GetNth(head1, 5, val) == true);
assert(val == 9);
assert(LL_GetNth(head1, 6, val) == true);
assert(val == 10);
assert(LL_GetNth(head1, 7, val) == true);
assert(val == 20);
assert(LL_GetNth(head1, 8, val) == true);
assert(val == 20);
assert(LL_GetNth(head1, 9, val) == true);
assert(val == 20);
assert(LL_GetNth(head1, 10, val) == true);
assert(val == 30);
assert(LL_GetNth(head1, 11, val) == true);
assert(val == 50);
assert(LL_GetNth(head1, 12, val) == false);

LL_MergeSort(&head2); // 6, 8, 9, 10, 10, 12, 12, 17, 18, 19, 56
assert(LL_GetNth(head2, 0, val) == true);
assert(val == 6);
assert(LL_GetNth(head2, 1, val) == true);
assert(val == 8);
assert(LL_GetNth(head2, 2, val) == true);
assert(val == 9);
assert(LL_GetNth(head2, 3, val) == true);
assert(val == 10);
assert(LL_GetNth(head2, 4, val) == true);
assert(val == 10);
assert(LL_GetNth(head2, 5, val) == true);
assert(val == 12);
assert(LL_GetNth(head2, 6, val) == true);
assert(val == 12);
assert(LL_GetNth(head2, 7, val) == true);
assert(val == 17);
assert(LL_GetNth(head2, 8, val) == true);
assert(val == 18);
assert(LL_GetNth(head2, 9, val) == true);
assert(val == 19);
assert(LL_GetNth(head2, 10, val) == true);
assert(val == 56);
assert(LL_GetNth(head2, 11, val) == false);

LinkedListElement<int>* front = nullptr;
LinkedListElement<int>* back = nullptr;
LL_FrontBackSplit(head1, &front, &back);
assert(front == head1);
assert(back->data == 10);
assert(LL_GetSize(front) == 6);
assert(LL_GetSize(back) == 6);
head1 = LL_SortedMerge(front, back); // 3, 4, 7, 7, 8, 9, 10, 20, 20, 20, 30, 50
assert(LL_GetSize(head1) == 12);
assert(LL_GetNth(head1, 0, val) == true);
assert(val == 3);
assert(LL_GetNth(head1, 1, val) == true);
assert(val == 4);
assert(LL_GetNth(head1, 2, val) == true);
assert(val == 7);
assert(LL_GetNth(head1, 3, val) == true);
assert(val == 7);
assert(LL_GetNth(head1, 4, val) == true);
assert(val == 8);
assert(LL_GetNth(head1, 5, val) == true);
assert(val == 9);
assert(LL_GetNth(head1, 6, val) == true);
assert(val == 10);
assert(LL_GetNth(head1, 7, val) == true);
assert(val == 20);
assert(LL_GetNth(head1, 8, val) == true);
assert(val == 20);
assert(LL_GetNth(head1, 9, val) == true);
assert(val == 20);
assert(LL_GetNth(head1, 10, val) == true);
assert(val == 30);
assert(LL_GetNth(head1, 11, val) == true);
assert(val == 50);
assert(LL_GetNth(head1, 12, val) == false);

LL_FrontBackSplit(head2, &front, &back); // 6, 8, 9, 10, 10, 12, 12, 17, 18, 19, 56
assert(front == head2);
assert(back->data == 12);
assert(LL_GetSize(front) == 6);
assert(LL_GetSize(back) == 5);
head2 = LL_SortedMergeRecursively(front, back);
assert(LL_GetNth(head2, 0, val) == true);
assert(val == 6);
assert(LL_GetNth(head2, 1, val) == true);
assert(val == 8);
assert(LL_GetNth(head2, 2, val) == true);
assert(val == 9);
assert(LL_GetNth(head2, 3, val) == true);
assert(val == 10);
assert(LL_GetNth(head2, 4, val) == true);
assert(val == 10);
assert(LL_GetNth(head2, 5, val) == true);
assert(val == 12);
assert(LL_GetNth(head2, 6, val) == true);
assert(val == 12);
assert(LL_GetNth(head2, 7, val) == true);
assert(val == 17);
assert(LL_GetNth(head2, 8, val) == true);
assert(val == 18);
assert(LL_GetNth(head2, 9, val) == true);
assert(val == 19);
assert(LL_GetNth(head2, 10, val) == true);
assert(val == 56);
assert(LL_GetNth(head2, 11, val) == false);

// 810, 9, 8
LinkedListElement<int>* intersect = LL_SortedIntersect(head1, head2);
assert(LL_GetSize(intersect) == 3);
assert(LL_GetNth(intersect, 0, val) == true);
assert(val == 10);
assert(LL_GetNth(intersect, 1, val) == true);
assert(val == 9);
assert(LL_GetNth(intersect, 2, val) == true);
assert(val == 8);
assert(LL_GetNth(intersect, 3, val) == false);
LL_Delete(&intersect);

// 3, 4, 6, 7, 7, 8, 8, 9, 9, 10, 10, 10, 12, 12, 17, 18, 19, 20, 20, 20, 30, 50, 56
LinkedListElement<int>* head = LL_SortedMergeRecursively(head1, head2);
assert(LL_GetSize(head) == 23);
assert(LL_GetNth(head, 0, val) == true);
assert(val == 3);
assert(LL_GetNth(head, 1, val) == true);
assert(val == 4);
assert(LL_GetNth(head, 2, val) == true);
assert(val == 6);
assert(LL_GetNth(head, 3, val) == true);
assert(val == 7);
assert(LL_GetNth(head, 4, val) == true);
assert(val == 7);
assert(LL_GetNth(head, 5, val) == true);
assert(val == 8);
assert(LL_GetNth(head, 6, val) == true);
assert(val == 8);
assert(LL_GetNth(head, 7, val) == true);
assert(val == 9);
assert(LL_GetNth(head, 8, val) == true);
assert(val == 9);
assert(LL_GetNth(head, 9, val) == true);
assert(val == 10);
assert(LL_GetNth(head, 10, val) == true);
assert(val == 10);
assert(LL_GetNth(head, 11, val) == true);
assert(val == 10);
assert(LL_GetNth(head, 12, val) == true);
assert(val == 12);
assert(LL_GetNth(head, 13, val) == true);
assert(val == 12);
assert(LL_GetNth(head, 14, val) == true);
assert(val == 17);
assert(LL_GetNth(head, 15, val) == true);
assert(val == 18);
assert(LL_GetNth(head, 16, val) == true);
assert(val == 19);
assert(LL_GetNth(head, 17, val) == true);
assert(val == 20);
assert(LL_GetNth(head, 18, val) == true);
assert(val == 20);
assert(LL_GetNth(head, 19, val) == true);
assert(val == 20);
assert(LL_GetNth(head, 20, val) == true);
assert(val == 30);
assert(LL_GetNth(head, 21, val) == true);
assert(val == 50);
assert(LL_GetNth(head, 22, val) == true);
assert(val == 56);
assert(LL_GetNth(head, 23, val) == false);

// 3, 4, 6, 7, 8, 9, 10, 12, 17, 18, 19, 20, 30, 50, 56
LL_RemoveDuplicates(&head);
assert(LL_GetSize(head) == 15);
assert(LL_GetNth(head, 0, val) == true);
assert(val == 3);
assert(LL_GetNth(head, 1, val) == true);
assert(val == 4);
assert(LL_GetNth(head, 2, val) == true);
assert(val == 6);
assert(LL_GetNth(head, 3, val) == true);
assert(val == 7);
assert(LL_GetNth(head, 4, val) == true);
assert(val == 8);
assert(LL_GetNth(head, 5, val) == true);
assert(val == 9);
assert(LL_GetNth(head, 6, val) == true);
assert(val == 10);
assert(LL_GetNth(head, 7, val) == true);
assert(val == 12);
assert(LL_GetNth(head, 8, val) == true);
assert(val == 17);
assert(LL_GetNth(head, 9, val) == true);
assert(val == 18);
assert(LL_GetNth(head, 10, val) == true);
assert(val == 19);
assert(LL_GetNth(head, 11, val) == true);
assert(val == 20);
assert(LL_GetNth(head, 12, val) == true);
assert(val == 30);
assert(LL_GetNth(head, 13, val) == true);
assert(val == 50);
assert(LL_GetNth(head, 14, val) == true);
assert(val == 56);
assert(LL_GetNth(head, 15, val) == false);

assert(LL_SortedInsert(&head, 1) == true);
// 1, 3, 4, 6, 7, 8, 9, 10, 12, 17, 18, 19, 20, 30, 50, 56
assert(LL_GetSize(head) == 16);
assert(LL_Find(head, 1) == 0);
// 1, 3, 4, 6, 7, 8, 9, 10, 12, 17, 18, 19, 20, 30, 50, 56, 60
assert(LL_SortedInsert(&head, 60) == true);
assert(LL_GetSize(head) == 17);
assert(LL_Find(head, 60) == 16);
// 1, 3, 4, 6, 7, 8, 9, 10, 10, 12, 17, 18, 19, 20, 30, 50, 56, 60
assert(LL_SortedInsert(&head, 10));
ptrdiff_t pos = LL_Find(head, 10);
assert(pos == 7);
pos = LL_Find(head, pos + 1, 10);
assert(pos == 0);

LL_Delete(&head);

}

//********************************************************************************

Bibliography:
[1] http://cslibrary.stanford.edu/105/LinkedListProblems.pdf
[2] Glenn W. Rowe, Data Structure & Algorithm C++, Prentice Hall, 1996
[3] http://en.wikipedia.org/wiki/Merge_sort
[4] http://en.wikipedia.org/wiki/Sorting_algorithm

Tuesday, 12 August 2014

Data Structure and Algorithm - Linked List: Common API

As I mentioned that Linked List is regarded as one of most frequently asked interview questions in Data Structure and Algorithm - Sort and Binary Search. One of the most beautiful things of these questions related to Linked List is to tell the interviewers how the candidate understands or grasps the concept and manipulation of pointer, which is regarded not an technical skill but an aptitude.

As I highlight in the following code, passing a pointer to a pointer "**" or passing a pointer "*" to LinkedListElement depends on what the function is to do. Any function is potentially to modify the argument head, a pointer to a pointer to LinkedListElement has to be passed, because the modification has to be made into the argument passed into the function. Otherwise a pointer to LinkedListElement should do the job.

// C Implementation of Linked List
//********************************************************************************
// LinkedListElement.h
#ifndef LINKED_LIST_ELEMENT_H
#define LINKED_LIST_ELEMENT_H

#pragma once

template <typename T>
struct LinkedListElement {
T data;
LinkedListElement<T>* next = nullptr;

LinkedListElement()
{}
LinkedListElement(const T& t) : data(t)
{}
~LinkedListElement()
{}
};

#endif

// LinkedListAlgo.h

#ifndef LINKED_LIST_ALGO_H

#define LINKED_LIST_ALGO_H

#pragma once

#include "LinkedListElement.h"

template<typename T>

void LL_PushFront(LinkedListElement<T>** head, const T& data)

{

if (*head == nullptr) {

*head = new LinkedListElement<T>(data);

}

else {

LinkedListElement<T>* curHead = *head;

*head = new LinkedListElement<T>(data);

(*head)->next = curHead;

}

template<typename T>

void LL_PushBack(LinkedListElement<T>** head, const T& data)

{

if (*head == nullptr) {

*head = new LinkedListElement<T>(data);

}

else {

LinkedListElement<T>* curHead = *head;

while (curHead->next != nullptr) {

curHead = curHead->next;

}

curHead->next = new LinkedListElement<T>(data);

}

template<typename T>

void LL_PopFront(LinkedListElement<T>** head)

{

if (head == nullptr || *head == nullptr) {

return;

}

LinkedListElement<T>* temp = *head;

*head = (*head)->next;

delete temp;

}

template<typename T>

void LL_PopBack(LinkedListElement<T>** head)

{

if (head == nullptr || *head == nullptr) {

return;

}

LinkedListElement<T>* prev = *head;

LinkedListElement<T>* curHead = *head;

while (curHead->next != nullptr) {

prev = curHead;

curHead = curHead->next;

}

prev->next = nullptr;

delete curHead;

}

template<typename T>

bool LL_Insert(LinkedListElement<T>** head, size_t pos, const T& data)

{

if (pos == 0) {

LL_PushFront(head, data);

return true;

}

LinkedListElement<T>* curHead = *head;

while (--pos > 0) {

curHead = curHead->next;

if (curHead == nullptr) {

return false;

}

LinkedListElement<T>* next = curHead->next;

curHead->next = new LinkedListElement<T>(data);

curHead->next->next = next;

return true;

}

template<typename T>

bool LL_Insert(LinkedListElement<T>** head, const LinkedListElement<T>* pos_node, const T& data)

{

if (head == nullptr || *head == nullptr || pos_node == nullptr) {

return false;

}

if (*head == pos_node) {

LL_PushFront(head, data);

return true;

}

LinkedListElement<T>* prev = nullptr;

LinkedListElement<T>* curHead = *head;

while (curHead != pos_node) {

prev = curHead;

curHead = curHead->next;

if (curHead == nullptr) {

return false;

}

prev->next = new LinkedListElement<T>(data);

prev->next->next = curHead;

return true;

}

template<typename T>

bool LL_Erase(LinkedListElement<T>** head, size_t pos)

{

if (head == nullptr || *head == nullptr) {

return false;

}

if (pos == 0) {

LL_PopFront(head);

return true;

}

LinkedListElement<T>* prev = *head;

LinkedListElement<T>* curHead = *head;

while (--pos > 0) {

prev = curHead;

curHead = curHead->next;

if (curHead == nullptr) {

return false;

}

prev->next = curHead->next;

delete curHead;

return true;

}

template<typename T>

bool LL_Erase(LinkedListElement<T>** head, const LinkedListElement<T>* pos_node)

{

if (head == nullptr || *head == nullptr || pos_node == nullptr) {

return false;

}

if (*head == pos_node) {

LL_PopFront(head);

return true;

}

LinkedListElement<T>* prev = nullptr;

LinkedListElement<T>* curHead = *head;

while (curHead != pos_node) {

prev = curHead;

curHead = curHead->next;

if (curHead == nullptr) {

return false;

}

prev->next = curHead->next;

delete curHead;

return true;

}

template<typename T>

bool LL_GetNth(LinkedListElement<T>* head, size_t pos, T& data)

{

if (head == nullptr) {

return false;

}

while (pos > 0) {

head = head->next;

if (head == nullptr) {

return false;

}

--pos;

}

data = head->data;

return true;

}

template<typename T>

LinkedListElement<T>* LL_GetNth(LinkedListElement<T>* head, size_t pos)

{

if (head == nullptr) {

return nullptr;

}

while (pos > 0) {

head = head->next;

if (head == nullptr) {

return nullptr;

}

--pos;

}

return head;

}

template<typename T>

size_t LL_GetSize(LinkedListElement<T>* head)

{

size_t size = 0;

while (head != nullptr) {

head = head->next;

++size;

}

return size;

}

template<typename T>

void LL_Reverse(LinkedListElement<T>** head)

{

// return if has less than 2 nodes

if (head == nullptr || *head == nullptr || (*head)->next == nullptr) {

return;

}

LinkedListElement<T>* cur = *head;

LinkedListElement<T>* next = nullptr;

LinkedListElement<T>* curHead = nullptr;

while (cur != nullptr) {

next = cur->next;

cur->next = curHead;

curHead = cur;

cur = next;

}

*head = curHead;

}

template<typename T>

void LL_Delete(LinkedListElement<T>** head)

{

if (head == nullptr || *head == nullptr) {

return;

}

LinkedListElement<T>* curHead = *head;

LinkedListElement<T>* temp = nullptr;

while (curHead != nullptr) {

temp = curHead;

curHead = curHead->next;

delete temp;

}

*head = nullptr;

}

* return -1, if not found

* 0 - size-1, if found the very first

template<typename T>

ptrdiff_t LL_Find(LinkedListElement<T>* head, const T& val)

{

if (head == nullptr) {

return -1;

}

ptrdiff_t pos = 0;

while (head != nullptr) {

if (head->data == val) {

return pos;

}

head = head->next;

++pos;

}

return -1;

}

template<typename T>

ptrdiff_t LL_Find(LinkedListElement<T>* head, size_t pos, const T& val)

{

if (head == nullptr) {

return -1;

}

while (pos > 0) {

head = head->next;

if (head == nullptr) {

return -1;

}

--pos;

}

return LL_Find(head, val);

}

#endif

// test.cpp

void TestLinkedListAlgo()

{

LinkedListElement<int>* head = nullptr;

// construct list: 20, 12, 10, 9, 9, 8, 7, 15

LL_PushFront(&head, 9);

LL_PushFront(&head, 10);

LL_PushFront(&head, 12);

LL_PushBack(&head, 9);

LL_PushBack(&head, 8);

LL_PushBack(&head, 7);

LL_PushBack(&head, 15);

LL_PushFront(&head, 20);

assert(LL_GetSize(head) == 8);

int val;

assert(LL_GetNth(head, 0, val) == true);

assert(val == 20);

assert(LL_GetNth(head, 1, val) == true);

assert(val == 12);

assert(LL_GetNth(head, 2, val) == true);

assert(val == 10);

assert(LL_GetNth(head, 3, val) == true);

assert(val == 9);

assert(LL_GetNth(head, 4, val) == true);

assert(val == 9);

assert(LL_GetNth(head, 5, val) == true);

assert(val == 8);

assert(LL_GetNth(head, 6, val) == true);

assert(val == 7);

assert(LL_GetNth(head, 7, val) == true);

assert(val == 15);

assert(LL_GetNth(head, 8, val) == false);

LL_PopFront(&head);

assert(LL_GetSize(head) == 7); // 12, 10, 9, 9, 8, 7, 15

LL_PopBack(&head);

assert(LL_GetSize(head) == 6); // 12, 10, 9, 9, 8, 7

LL_Delete(&head);

// constuct list: 18, 25, 30, 11, 10, 9, 5, 20

LL_PushBack(&head, 10);

LL_PushBack(&head, 9);

LL_PushBack(&head, 5);

LL_PushBack(&head, 20);

LL_PushFront(&head, 11);

LL_PushFront(&head, 30);

LL_PushFront(&head, 25);

LL_PushFront(&head, 18);

assert(LL_GetSize(head) == 8);

assert(LL_Insert(&head, 0, 40) == true); // 40, 18, 25, 30, 11, 10, 9, 5, 20

assert(LL_GetSize(head) == 9);

assert(LL_GetNth(head, 0, val) == true);

assert(val = 40);

assert(LL_Insert(&head, 10, 50) == false);

assert(LL_GetSize(head) == 9);

assert(LL_Insert(&head, 9, 50) == true); // 40, 18, 25, 30, 11, 10, 9, 5, 20, 50

assert(LL_GetSize(head) == 10);

assert(LL_GetNth(head, 9, val) == true);

assert(val == 50);

assert(LL_Insert(&head, 3, 100) == true); // 40, 18, 25, 100, 30, 11, 10, 9, 5, 20, 50

assert(LL_GetSize(head) == 11);

assert(LL_GetNth(head, 3, val) == true);

assert(val == 100);

LinkedListElement<int>* elemPtr = LL_GetNth(head, 2); // index starts from 0

assert(elemPtr != nullptr);

assert(elemPtr->data == 25);

assert(LL_GetNth(head, 11) == nullptr);

elemPtr = LL_GetNth(head, 9);

assert(elemPtr != nullptr);

assert(elemPtr->data == 20);

assert(LL_Insert(&head, elemPtr, 70) == true); // 40, 18, 25, 100, 30, 11, 10, 9, 5, 70, 20, 50

assert(LL_GetSize(head) == 12);

elemPtr = LL_GetNth(head, 9);

assert(elemPtr != nullptr);

assert(elemPtr->data == 70);

assert(LL_GetNth(head, 3, val) == true);

assert(val == 100);

assert(LL_GetNth(head, 12, val) == false);

assert(LL_GetSize(head) == 12);

assert(LL_Erase(&head, 0) == true); // 18, 25, 100, 30, 11, 10, 9, 5, 70, 20, 50

assert(LL_GetSize(head) == 11);

elemPtr = LL_GetNth(head, 0);

assert(elemPtr != nullptr);

assert(elemPtr->data == 18);

elemPtr = LL_GetNth(head, 10);

assert(elemPtr != nullptr);

assert(elemPtr->data == 50);

assert(LL_Erase(&head, elemPtr)); // 18, 25, 100, 30, 11, 10, 9, 5, 70, 20

assert(LL_GetSize(head) == 10);

assert(LL_GetNth(head, 10, val) == false);

assert(LL_GetNth(head, 9, val) == true);

assert(val == 20);

LL_PopFront(&head); // 25, 100, 30, 11, 10, 9, 5, 70, 20

assert(LL_GetSize(head) == 9);

elemPtr = LL_GetNth(head, 0);

assert(elemPtr != nullptr);

assert(elemPtr->data == 25);

LL_PopBack(&head); // 25, 100, 30, 11, 10, 9, 5, 70

assert(LL_GetSize(head) == 8);

assert(LL_GetNth(head, 8, val) == false);

assert(LL_GetNth(head, 7, val) == true);

assert(val == 70);

LL_Reverse(&head); // 70, 5, 9, 10, 11, 30, 100, 25

assert(LL_GetSize(head) == 8);

assert(LL_GetNth(head, 0, val) == true);

assert(val == 70);

assert(LL_GetNth(head, 1, val) == true);

assert(val == 5);

assert(LL_GetNth(head, 2, val) == true);

assert(val == 9);

assert(LL_GetNth(head, 3, val) == true);

assert(val == 10);

assert(LL_GetNth(head, 4, val) == true);

assert(val == 11);

assert(LL_GetNth(head, 5, val) == true);

assert(val == 30);

assert(LL_GetNth(head, 6, val) == true);

assert(val == 100);

assert(LL_GetNth(head, 7, val) == true);

assert(val == 25);

assert(LL_Insert(&head, 2, 10) == true); // 70, 5, 10, 9, 10, 11, 30, 100, 25

ptrdiff_t pos = LL_Find(head, 70);

assert(pos == 0);

pos = LL_Find(head, 25);

assert(pos == 8);

pos = LL_Find(head, 30);

assert(pos == 6);

pos = LL_Find(head, 10);

assert(pos == 2);

pos = LL_Find(head, 2, 10);

assert(pos == 0);

pos = LL_Find(head, 3, 10);

assert(pos == 1);

pos = LL_Find(head, 50);

assert(pos == -1);

LL_Delete(&head);

assert(head == nullptr);

assert(LL_GetSize(head) == 0);

}