// Leetcode24.cpp : This file contains the 'main' function. Program execution begins and ends there.

//

#include <iostream>

#include <vector>

using namespace::std;

struct ListNode

{

int val;

ListNode* next;

ListNode() : val(0), next(nullptr) {}

ListNode(int x) : val(x), next(nullptr) {}

ListNode(int x, ListNode* next) : val(x), next(next) {}

};

ListNode* listCreate(vector<int>& v)

{

ListNode* p = nullptr, * t = nullptr;

for (auto vi : v)

{

//int a = 1;

//int* pa = &a;

ListNode* node = new ListNode(vi);

//ListNode node = ListNode(vi);

if (p == nullptr)

p = node;

if (t == nullptr)

t = node;

else

{

t->next = node;

t = node;

}

}

return p;

}

ListNode* swapPairs(ListNode* head)

{

if (head == nullptr)

return nullptr;

if (head->next == nullptr)

return head;

ListNode* begin = head, * tail = nullptr, * leftBegin = head;

begin = head->next;

ListNode* temp = nullptr;

while (leftBegin->next != nullptr)

{

ListNode* leftBegin2 = leftBegin->next;

temp = leftBegin2->next;

leftBegin2->next = leftBegin;

leftBegin->next = temp;

if(tail)

tail->next = leftBegin2;

tail = leftBegin;

leftBegin = temp;

if (tail->next == nullptr)

break;

}

tail->next = leftBegin;

return begin;

}

int main()

{

vector<int> vi = { 1,2,3,4,5 };

ListNode* pl = listCreate(vi);

ListNode* res = swapPairs(pl);

std::cout << "Hello World!\n";

}

// Run program: Ctrl + F5 or Debug > Start Without Debugging menu

// Debug program: F5 or Debug > Start Debugging menu

// Tips for Getting Started:

// 1. Use the Solution Explorer window to add/manage files

// 2. Use the Team Explorer window to connect to source control

// 3. Use the Output window to see build output and other messages

// 4. Use the Error List window to view errors

// 5. Go to Project > Add New Item to create new code files, or Project > Add Existing Item to add existing code files to the project

// 6. In the future, to open this project again, go to File > Open > Project and select the .sln file