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.

分析：

将两两相邻的节点交换值，题目简单，只需记录前一个节点的值即可

/**
 * 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 *l=head;
        while(l!=NULL&&l->next!=NULL){
            int n=l->val;
            l->val=l->next->val;
            l->next->val=n;
            l=l->next->next;
        }
        return head;
    }
};