【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=0,tmp=0;
    struct ListNode* p=head;
    while(p!=NULL){
        if(0==flag&&p->next!=NULL){
            tmp=p->val;
            p->val=p->next->val;
            flag=1;
        }
        else if(1==flag){
            p->val=tmp;
            flag=0;
        }
        p=p->next;
    }
    return head;
}