Leetcode笔记（Linked List）——Swap Nodes in Pairs(24)

Problem

Given a linked list, swap every two adjacent nodes and return its head.

Example

Given 1->2->3->4, you should return the list as 2->1->4->3.

Solution

/**
 * 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) {    
            
             ListNode **pp = &head, *a, *b;
             while ((a = *pp) && (b = a->next)) {
                   a->next = b->next;
                   b->next = a;
                   *pp = b;
                   pp = &(a->next);
             }
             return head;

    }
};