Swap Nodes in Pairs

 1 /**
 2  * Definition for singly-linked list.
 3  * struct ListNode {
 4  *     int val;
 5  *     ListNode *next;
 6  *     ListNode(int x) : val(x), next(NULL) {}
 7  * };
 8  */
 9 class Solution {
10 public:
11     ListNode* swapPairs(ListNode* head) {
12         if(head==NULL||head->next==NULL)
13         return head;
14         ListNode *pre,*lat,*p;
15          ListNode *tmp;//=(ListNode*)malloc(sizeof(ListNode));
16         pre=head;
17         lat=head->next;p=head->next;
18         while(1)
19         {
20             tmp->next=lat;
21             pre->next=lat->next;
22             lat->next=pre;tmp=pre;
23             pre=pre->next;
24             if(pre==NULL)
25             break;
26             lat=pre->next;
27             if(lat==NULL)
28             break;
29            
30         }
31         return p;
32         
33     }
34 };