[Leetcode 24 链表]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.

加个表头节点，各种清晰。

class Solution {    public:    ListNode *swapPairs(ListNode *head) {        ListNode nodehead(0);        ListNode *pmove = &nodehead;        nodehead.next = head;        //if have only one node,won't go into while        ListNode *first = head;        ListNode *second = head?head->next:NULL; //head may be NULL        while(first && second)        {            first->next = second->next;            second->next = first;            pmove->next = second;            pmove = first;            first = first?first->next:NULL;            second = first?first->next:NULL;        }        return nodehead.next;    }};