1 public class Main {
2
3 // 就地逆序法
4 public Node reverse(Node head) {
5 // no need to reverse
6 if (head == null || head.next == null || head.next.next == null) {
7 return head;
8 }
9
10 // pointer
11 Node pre = head;
12 Node cur = head.next;
13 Node nex = head.next.next;
14
15 while (nex != null) {
16 if (cur == head.next) // the first node's next node is null
17 {
18 cur.next = null;
19 } else {
20 cur.next = pre;
21 }
22
23 pre = cur;
24 cur = nex;
25 nex = nex.next;
26 }
27
28 cur.next = pre;
29 head.next = cur;
30
31 return head;
32 }
33
34 // 插入法
35 public Node reverse2(Node head) {
36 if (head == null || head.next == null) {
37 return head;
38 }
39
40 Node p1 = head.next;
41
42 Node p = null;
43
44 while (p1.next != null) {
45 p = p1.next;
46 p1.next = p.next;
47 p.next = head.next;
48 head.next = p;
49 }
50
51 return head;
52 }
53
54 public Node createListNodes() {
55 Node node7 = new Node(7, null);
56 Node node6 = new Node(6, node7);
57 Node node5 = new Node(5, node6);
58 Node node4 = new Node(4, node5);
59 Node node3 = new Node(3, node4);
60 Node node2 = new Node(2, node3);
61 Node node1 = new Node(1, node2);
62 Node head = new Node(0, node1); // head pointer
63
64 return head;
65 }
66
67 public static void main(String[] args) {
68 Main main = new Main();
69 Node node = main.reverse(main.createListNodes());
70
71 if (node == null) {
72 System.out.println("head is null");
73 return;
74 }
75
76 while (node.next != null) {
77 System.out.println(node.next.data);
78 node = node.next;
79 }
80
81 Node node2 = main.reverse2(main.createListNodes());
82
83 if (node2 == null) {
84 System.out.println("head is null");
85 return;
86 }
87
88 while (node2.next != null) {
89 System.out.println(node2.next.data);
90 node2 = node2.next;
91 }
92 }
93
94 }
