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24.swap-nodes-in-pairs.c
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24.swap-nodes-in-pairs.c
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/*
* @lc app=leetcode id=24 lang=c
*
* [24] Swap Nodes in Pairs
*/
struct ListNode
{
int val;
struct ListNode *next;
};
// @lc code=start
/**
* Definition for singly-linked list.
* struct ListNode {
* int val;
* struct ListNode *next;
* };
*/
#include <stdlib.h>
struct ListNode *swapPairs(struct ListNode *head)
{
if (head == NULL || head->next == NULL)
{
return head;
}
struct ListNode *current = head;
struct ListNode *pre = NULL;
while (current != NULL && current->next != NULL)
{
struct ListNode *next = current->next;
current->next = next->next;
next->next = current;
if (current == head)
{
head = next;
}
if (pre != NULL)
{
pre->next = next;
}
pre = current;
current = current->next;
}
return head;
}
// @lc code=end
#include <stdio.h>
int main(int argc, char const *argv[])
{
struct ListNode *head = malloc(sizeof(struct ListNode) * 4);
head->val = 1;
head->next = &head[1];
head[1].val = 2;
head[1].next = &head[2];
head[2].val = 3;
head[2].next = &head[3];
head[3].val = 4;
head[3].next = NULL;
head = swapPairs(head);
while (head != NULL)
{
printf("head value is %d \n", head->val);
head = head->next;
}
return 0;
}