二叉树的遍历

 1 import java.util.LinkedList;
 2 
 3 public class BinaryTreeErgodic {
 4 
 5     /**
 6      * 层次优先遍历
 7      */
 8     public static void lavelOrderTraverse(TreeNode root) {
 9         if (root == null)
10             return;
11 
12         LinkedList<TreeNode> queue = new LinkedList<TreeNode>();
13         TreeNode current = null;
14         queue.offer(root);
15         while (!queue.isEmpty()) {
16             current = queue.poll();
17             System.out.print(current.value + " ");
18             if (current.left != null)
19                 queue.offer(current.left);
20             if (current.right != null)
21                 queue.offer(current.right);
22         }
23     }
24 
25     /**
26      * 先序遍历
27      */
28     public static void preOrderTraverse(TreeNode node) {
29         if (node == null)
30             return;
31         System.out.print(node.value + " ");
32         preOrderTraverse(node.left);
33         preOrderTraverse(node.right);
34     }
35 
36     /**
37      * 中序遍历
38      */
39     public static void inOrderTraverse(TreeNode node) {
40         if (node == null)
41             return;
42         inOrderTraverse(node.left);
43         System.out.print(node.value + " ");
44         inOrderTraverse(node.right);
45     }
46 
47     /**
48      * 后序遍历
49      */
50     public static void postOrderTraverse(TreeNode node) {
51         if (node == null)
52             return;
53         postOrderTraverse(node.left);
54         postOrderTraverse(node.right);
55         System.out.print(node.value + " ");
56     }
57 }
58 
59 class TreeNode {
60 
61     int value;
62 
63     public TreeNode(int value) {
64         this.value = value;
65     }
66 
67     TreeNode left = null;
68     TreeNode right = null;
69 }
上述代码分别实现了二叉树的：层次优先遍历、前序遍历（先序遍历）、中序遍历、后序遍历，具体原理大家都明白