1 package tree;
 2
 3 import java.util.LinkedList;
 4 import java.util.List;
 5
 6 public class Tree {
 7
 8     private static class Node{
 9         Node left;
10         Node right;
11         int val;
12
13         Node(int data){
14             left = null;
15             right = null;
16             val = data;
17         }
18     }
19
20     //生成一颗二叉树
21     public static List<Node> CreatTree(int[] array){
22
23         List<Node> nodelist = new LinkedList<>();
24         //每个位置转换成节点
25         for(int i = 0; i<array.length; i++){
26             nodelist.add(new Node(array[i]));
27         }
28         //按照关系建立二叉树
29         for(int i=0; i<array.length/2-1; i++){
30             //左孩子
31             nodelist.get(i).left = nodelist.get(i*2+1);
32             //右孩子
33             nodelist.get(i).right = nodelist.get(i*2+2);
34         }
35         //最后一个节点特殊处理
36         int index = array.length / 2 - 1;
37         //左孩子
38         nodelist.get(index).left = nodelist.get(index*2+1);
39         //如果长度是奇数，那就有右孩子
40         if(array.length%2 == 1){
41             nodelist.get(index).right = nodelist.get(index*2+2);
42         }
43
44         return nodelist;
45     }
46
47     //先序遍历（根、左、右）
48     public static void preOrderTraverse(Node node){
49         if(node == null) return;
50         //根
51         System.out.print(node.val + " ");
52         //左
53         preOrderTraverse(node.left);
54         //右
55         preOrderTraverse(node.right);
56     }
57
58     //中序遍历
59     public static void inOrderTraverse(Node node){
60         if(node == null) return;
61         //左
62         inOrderTraverse(node.left);
63         //根
64         System.out.print(node.val + " ");
65         //右
66         inOrderTraverse(node.right);
67     }
68
69     //后序遍历
70     public static void postOrderTraverse(Node node){
71         if(node == null) return;
72         //左
73         postOrderTraverse(node.left);
74         //右
75         postOrderTraverse(node.right);
76         //根
77         System.out.print(node.val + " ");
78     }
79
80
81     public static void main(String[] args) {
82         int[] array = { 1, 2, 3, 4, 5, 6, 7, 8 };
83         //获取根节点
84         Node root = Tree.CreatTree(array).get(0);
85
86         System.out.println("先序遍历：");
87         preOrderTraverse(root);
88         System.out.println();
89
90         System.out.println("中序遍历：");
91         inOrderTraverse(root);
92         System.out.println();
93
94         System.out.println("后序遍历：");
95         postOrderTraverse(root);
96         System.out.println();
97     }
98
99 }