1 const bt = {
2 val: 1,
3 left: {
4 val: 2,
5 left: {
6 val: 4,
7 left: null,
8 right: null,
9 },
10 right: {
11 val: 5,
12 left: null,
13 right: null,
14 },
15 },
16 right: {
17 val: 3,
18 left: {
19 val: 6,
20 left: null,
21 right: null,
22 },
23 right: {
24 val: 7,
25 left: null,
26 right: null,
27 },
28 },
29 };
30
31 //可以用堆栈来模拟递归
32
33 //先序遍历
34 const preorder = (root) => {
35 if(!root) {return; }
36 const stack = [root]; //创建一个栈
37 while (stack.length) {
38 const n = stack.pop();
39 console.log(n.val);
40 if(n.right) stack.push(n.right); //根左右，栈是后进先出，所以先把右结点压栈
41 if(n.left) stack.push(n.left);
42 }
43 }
44 preorder(bt)
45
46 //中序遍历
47 const inorder = (root) => {
48 if(!root) {return; }
49 const stack = []; //创建一个栈
50 let p = root;
51 while(stack.length || p) {
52 while(p) {
53 stack.push(p); //左根右,遍历所以左结点压入栈中
54 p = p.left;
55 }
56 const n = stack.pop();
57 console.log(n.val); //弹出就是 左结点和中结点
58 p = n.right; //把右结点压入，参与循环
59 }
60 }
61
62 inorder(bt);
63
64 //后序遍历
65 const postorder = (root) => { //后序遍历是左 右 根，先序遍历得到的是根 左 右
66 if(!root) {return; } // 把前序遍历的顺序调换一下得到 根 右 左，压栈再弹出就变成了 左 右 根
67 const outputStack = [];
68 const stack = [root]; //需要两个栈
69 while (stack.length) {
70 const n = stack.pop();
71 outputStack.push(n);
72 if(n.left) stack.push(n.left);
73 if(n.right) stack.push(n.right);
74 }
75 while(outputStack.length) { //倒叙输出即可
76 const n = outputStack.pop();
77 console.log(n.val);
78 }
79 }
80
81 postorder(bt);
