leetcode|24. Swap Nodes in Pairs

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

Note:

• Your algorithm should use only constant extra space.
• You may not modify the values in the list's nodes, only nodes itself may be changed

主要考察交换两个节点的顺序

从现在开始尝试所有代码都用Java写了！！！

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
class Solution {
    public ListNode swapPairs(ListNode head) {
        //交换链表中两个节点
        ListNode dummy=new ListNode(0);
        dummy.next=head;
        ListNode current=dummy;
        while(current.next!=null&&current.next.next!=null){
            ListNode first=current.next;
            ListNode second=current.next.next;
            current.next=second;
            first.next=second.next;
            second.next=first;
            current=current.next.next;
        }
        return dummy.next;
        
    }
}