https://leetcode.com/problems/swap-nodes-in-pairs/description/
输入: 一个链表
输出: 每两位颠倒
要求: 不能使用额外空间,不能修改节点的值,只能修改引用
思路: 循环修改 next 即可,一次 AC
/**
* Definition for singly-linked list.
* public class ListNode {
* int val;
* ListNode next;
* ListNode(int x) { val = x; }
* }
*/
class Solution {
public ListNode swapPairs(ListNode head) {
ListNode current=head,next,nextnext;
ListNode result=new ListNode(-1);
ListNode pre=result;
result.next = head;
while(current!=null&&(next=current.next)!=null){
nextnext = next.next;
pre.next=next;
next.next=current;
current.next=nextnext;
pre=current;
current = nextnext;
}
return result.next;
}
}
