[C语言][LeetCode][24]Swap Nodes in Pairs

题目

Swap Nodes in Pairs

Given a linked list, swap every two adjacent nodes and return its head.

For example,

Given 1->2->3->4, you should return the list as 2->1->4->3.

Your algorithm should use only constant space. You may not modify the values in the list, only nodes itself can be changed.

标签

Linked List

难度

简单

分析

题目意思是给定一个单链表，交换两个相邻的节点。我的做法是先找到新链表的头结点，然后像交换两个变量的值的方式，来交换两个相邻的节点，这里需要注意的是，交换的时候，需要保存交换节点的前后节点，这里我用left、right去保存，为了交换之后，前后节点不丢失。

C代码实现

struct ListNode* swapPairs(struct ListNode* head)
{
struct ListNode *p, *q, *right, *left;
struct ListNode * ret;

if(!head || !head->next)
return head;

p = head;
q = p->next;

if(p && q)
ret = q;

while(p && q)
{
right = q->next;
q->next = p;
left = p;
p->next = right;
p = right;

if(!right || !right->next)
break;

if(right->next)
{
q = p->next;
left->next = q;
}
}

return ret;
}