1 package com.algorithm;
2
3 //输入一个链表，反转链表后，输出链表的所有元素。
4 public class ReverseListMe {
5
6 public ListNode ReverseList(ListNode head) {
7 //运行时间：36ms 占用内存：528k
8 if(head == null) {
9 return head;
10 }
11 if(head.next == null) {
12 System.out.println(head.val);
13 return head;
14 }
15 ListNode front = head;//前一个
16 ListNode back = head.next;//后一个
17 ListNode guard = back.next;//第三个
18 front.next = null;//将最后一个赋值为null
19 while(back != null) {
20 back.next = front;//把第二项的next 赋值为front
21 front = back;
22 back = guard;//将guard 赋值给front
23 if(guard != null)
24 guard = guard.next;//将guade的next赋值给guard
25 }
26 head = front;
27 while(front != null) {
28 System.out.println(front.val);
29 front = front.next;
30 }
31 return head;
32 }
33 public static void main(String[] args) {
34 ListNode la = new ListNode(1);
35 ListNode lb = new ListNode(2);
36 ListNode lc = new ListNode(3);
37 la.next = lb;
38 lb.next = lc;
39 lc.next = null;
40 new ReverseListMe().ReverseList(la);
41 }
42 /*class ListNode {
43 int val;
44 ListNode next = null;
45 ListNode(int val) {
46 this.val = val;
47 }
48 }*/
49 }
1 ListNode pre = null;
2 ListNode next = null;
3 while (head != null) {
4 next = head.next;
5 head.next = pre;
6 pre = head;
7 head = next;
8 }
9 return pre;
