LeetCode 24. 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.

题目比较简单，直接上代码了。

/**
* Definition for singly-linked list.
* struct ListNode {
* int val;
* ListNode *next;
* ListNode(int x) : val(x), next(NULL) {}
* };
*/
class Solution {
public:
ListNode* swapPairs(ListNode* head)
{
if(head == NULL || head->next == NULL)
return head;
ListNode *p,*q,*pnext;
p = head;
q = p->next;
pnext = q->next;
int temp = p->val;
p->val = q ->val;
q ->val = temp;
while(pnext != NULL && pnext->next != NULL)
{
int temp =pnext ->val;
ListNode *s = pnext->next;
pnext->val = s->val;
s->val = temp;
pnext = s->next;
}

return head;

}

};