二叉树的三种遍历递归和非递归实现

摘自《数据结构C++版》，用java实现：

1. package JobInterview_01;
3. import java.util.Stack;
5. public class BinaryRecursive {
6. public static class Node {
7. public int value;
8. public Node left;
9. public Node right;
11. public Node(int data) {
12. this.value = data;
13. }
15. }
17. // 前序遍历
18. public static void preOrderRecur(Node head) {
19. if (head == null) {
20. return;
21. }
22. System.out.print(head.value + " ");
23. preOrderRecur(head.left);
24. preOrderRecur(head.right);
25. }
27. // 中序遍历
28. public static void inOrderRecur(Node head) {
29. if (head == null) {
30. return;
31. }
32. inOrderRecur(head.left);
33. System.out.print(head.value + " ");
34. inOrderRecur(head.right);
36. }
38. // 后序遍历
39. public static void posOrderRecur(Node head) {
40. if (head == null) {
41. return;
42. }
43. posOrderRecur(head.left);
44. posOrderRecur(head.right);
45. System.out.print(head.value + " ");
47. }
48. //非递归 前序遍历
49. public static void preOrderUnrecur(Node head){
50. System.out.println("pre-oder unrecur: ");
51. if (head != null) {
52. Stack<Node> stack = new Stack<Node>();
53. stack.add(head);
54. while(!stack.isEmpty()){
55. head = stack.pop();
56. System.out.print(head.value+" ");
57. if (head.right!= null) {
58. stack.push(head.right);
59. }
60. if (head.left != null) {
61. stack.push(head.left);
62. }
63. }
64. }
65. System.out.println();
66. }
67. //非递归 中序遍历
68. public static void inOrderUnrecur(Node head){
69. System.out.println("in-order unrecur:");
70. if (head != null) {
71. Stack<Node> stack = new Stack<Node>();
72. while (!stack.isEmpty() || head != null) {
73. if(head != null){
74. stack.push(head);
75. head = head.left;
76. }
77. else {
78. head = stack.pop();
79. System.out.print(head.value+" ");
80. head = head.right;
81. }
82. }
83. }
84. System.out.println();
85. }
86. public static void posOrderUnRecur1(Node head) {
87. System.out.print("pos-order unrecur: ");
88. if (head != null) {
89. Stack<Node> s1 = new Stack<Node>();
90. Stack<Node> s2 = new Stack<Node>();
91. s1.push(head);
92. while (!s1.isEmpty()) {
93. head = s1.pop();
94. s2.push(head);
95. if (head.left != null) {
96. s1.push(head.left);
97. }
98. if (head.right != null) {
99. s1.push(head.right);
100. }
101. }
102. while (!s2.isEmpty()) {
103. System.out.print(s2.pop().value + " ");
104. }
105. }
106. System.out.println();
107. }
109. public static void main(String[] args) {
110. Node head = new Node(5);
111. head.left = new Node(3);
112. head.right = new Node(8);
113. head.left.left = new Node(2);
114. head.left.right = new Node(4);
115. head.left.left.left = new Node(1);
116. head.right.left = new Node(7);
117. head.right.left.left = new Node(6);
118. head.right.right = new Node(10);
119. head.right.right.left = new Node(9);
120. head.right.right.right = new Node(11);
123. preOrderRecur(head);
124. System.out.println();
125. preOrderUnrecur(head);
127. System.out.println("in-order:");
128. inOrderRecur(head);
129. System.out.println();
130. inOrderUnrecur(head);
132. System.out.println("pos order :");
133. posOrderRecur(head);
134. System.out.println();
135. posOrderUnRecur1(head);
137. }
139. }