LeetCode 24. Swap Nodes in Pairs

题目描述:

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.

交换链表相邻节点。

C++:

class Solution {
public:
    ListNode *swapPairs(ListNode *head) {
        if(head == NULL || head->next == NULL) return head;
        ListNode *first = head, *second = head->next, *prev = NULL;
        first->next = second->next;
        second->next = first;
        head = second;
        prev = first;
        first = first->next;
        while(first){
            second = first->next;
            if(second == NULL)break;
            first->next = second->next;
            second->next = first;
            prev->next = second;
            prev = first;
            first = first->next;
        }
        return head;
    }
};

时间4ms。