【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.

题意：倒转链表中相邻的两个值

 /**
  * Definition for singly-linked list.
  * struct ListNode {
  *     int val;
  *     struct ListNode *next;
  * };
  */
 struct ListNode* swapPairs(struct ListNode* head) {
     int flag=,tmp=;
     struct ListNode* p=head;
     while(p!=NULL){
         if(==flag&&p->next!=NULL){
             tmp=p->val;
             p->val=p->next->val;
             flag=;
         }
         else if(==flag){
             p->val=tmp;
             flag=;
         }
         p=p->next;
     }
     return head;
 }