Java实现二叉树先序，中序，后序遍历

以下是我要解析的一个二叉树的模型形状

接下来废话不多直接上代码

一种是用递归的方法，另一种是用堆栈的方法：

首先创建一棵树：

节点对象：

 1 public class Node {
 2   //节点数值
 3   private int data;
 4   //左子节点
 5   private Node leftNode;
 6   //右子节点
 7   private Node rightNode;
 8
 9   public Node(int data, Node leftNode, Node rightNode) {
10     this.data = data;
11     this.leftNode = leftNode;
12     this.rightNode = rightNode;
13   }
14
15   public int getData() {
16     return data;
17   }
18
19   public void setData(int data) {
20     this.data = data;
21   }
22
23   public Node getLeftNode() {
24     return leftNode;
25   }
26
27   public void setLeftNode(Node leftNode) {
28     this.leftNode = leftNode;
29   }
30
31   public Node getRightNode() {
32     return rightNode;
33   }
34
35   public void setRightNode(Node rightNode) {
36     this.rightNode = rightNode;
37   }
38 }

递归方式，实现树的遍历：

 1 public class BinaryTreeWithNode1 {
 2
 3   /**
 4    * 二叉树的先序中序后序排序
 5    */
 6   public Node init() {//注意必须逆序建立，先建立子节点，再逆序往上建立，因为非叶子结点会使用到下面的节点，而初始化是按顺序初始化的，不逆序建立会报错
 7     Node J = new Node(8, null, null);
 8     Node H = new Node(4, null, null);
 9     Node G = new Node(2, null, null);
10     Node F = new Node(7, null, J);
11     Node E = new Node(5, H, null);
12     Node D = new Node(1, null, G);
13     Node C = new Node(9, F, null);
14     Node B = new Node(3, D, E);
15     Node A = new Node(6, B, C);
16     return A;   //返回根节点
17   }
18
19   public void printNode(Node node) {
20     System.out.print(node.getData());
21   }
22
23   public void theFirstTraversal(Node root) {  //先序遍历
24     printNode(root);
25     if (root.getLeftNode() != null) {  //使用递归进行遍历左孩子
26       theFirstTraversal(root.getLeftNode());
27     }
28     if (root.getRightNode() != null) {  //递归遍历右孩子
29       theFirstTraversal(root.getRightNode());
30     }
31   }
32
33   public void theInOrderTraversal(Node root) {  //中序遍历
34     if (root.getLeftNode() != null) {
35       theInOrderTraversal(root.getLeftNode());
36     }
37     printNode(root);
38     if (root.getRightNode() != null) {
39       theInOrderTraversal(root.getRightNode());
40     }
41   }
42
43
44   public void thePostOrderTraversal(Node root) {  //后序遍历
45     if (root.getLeftNode() != null) {
46       thePostOrderTraversal(root.getLeftNode());
47     }
48     if (root.getRightNode() != null) {
49       thePostOrderTraversal(root.getRightNode());
50     }
51     printNode(root);
52   }
53
54   public static void main(String[] args) {
55     BinaryTreeWithNode1 tree = new BinaryTreeWithNode1();
56     Node root = tree.init();
57     System.out.println("先序遍历");
58     tree.theFirstTraversal(root);
59     System.out.println("");
60     System.out.println("中序遍历");
61     tree.theInOrderTraversal(root);
62     System.out.println("");
63     System.out.println("后序遍历");
64     tree.thePostOrderTraversal(root);
65     System.out.println("");
66   }
67
68 }

堆栈方式，实现树的遍历：

 1 import java.util.Stack;
 2
 3
 4 public class BinaryTreeWithNode2 {
 5
 6
 7   public Node init() {//注意必须逆序建立，先建立子节点，再逆序往上建立，因为非叶子结点会使用到下面的节点，而初始化是按顺序初始化的，不逆序建立会报错
 8     Node J = new Node(8, null, null);
 9     Node H = new Node(4, null, null);
10     Node G = new Node(2, null, null);
11     Node F = new Node(7, null, J);
12     Node E = new Node(5, H, null);
13     Node D = new Node(1, null, G);
14     Node C = new Node(9, F, null);
15     Node B = new Node(3, D, E);
16     Node A = new Node(6, B, C);
17     return A;   //返回根节点
18   }
19
20   public void printNode(Node node) {
21     System.out.print(node.getData());
22   }
23
24
25   public void theFirstTraversal_Stack(Node root) {  //先序遍历
26     Stack<Node> stack = new Stack<Node>();
27     Node node = root;
28     while (node != null || stack.size() > 0) {  //将所有左孩子压栈
29       if (node != null) {   //压栈之前先访问
30         printNode(node);
31         stack.push(node);
32         node = node.getLeftNode();
33       } else {
34         node = stack.pop();
35         node = node.getRightNode();
36       }
37     }
38   }
39
40   public void theInOrderTraversal_Stack(Node root) {  //中序遍历
41     Stack<Node> stack = new Stack<Node>();
42     Node node = root;
43     while (node != null || stack.size() > 0) {
44       if (node != null) {
45         stack.push(node);   //直接压栈
46         node = node.getLeftNode();
47       } else {
48         node = stack.pop(); //出栈并访问
49         printNode(node);
50         node = node.getRightNode();
51       }
52     }
53   }
54
55   public void thePostOrderTraversal_Stack(Node root) {   //后序遍历
56     Stack<Node> stack = new Stack<Node>();
57     Stack<Node> output = new Stack<Node>();//构造一个中间栈来存储逆后序遍历的结果
58     Node node = root;
59     while (node != null || stack.size() > 0) {
60       if (node != null) {
61         output.push(node);
62         stack.push(node);
63         node = node.getRightNode();
64       } else {
65         node = stack.pop();
66         node = node.getLeftNode();
67       }
68     }
69     System.out.println(output.size());
70     while (output.size() > 0) {
71
72       printNode(output.pop());
73     }
74   }
75
76   public static void main(String[] args) {
77     BinaryTreeWithNode2 tree = new BinaryTreeWithNode2();
78     Node root = tree.init();
79     System.out.println("先序遍历");
80     tree.theFirstTraversal_Stack(root);
81     System.out.println("");
82     System.out.println("中序遍历");
83     tree.theInOrderTraversal_Stack(root);
84     System.out.println("");
85     System.out.println("后序遍历");
86     tree.thePostOrderTraversal_Stack(root);
87     System.out.println("");
88   }
89
90
91 }

原文出处：Java实现二叉树先序，中序，后序遍历

原文地址：https://www.cnblogs.com/betterboyz/p/9205118.html