[LeetCode][JavaScript]Binary Tree Inorder Traversal

Binary Tree Inorder Traversal

Given a binary tree, return the inorder traversal of its nodes‘ values.

For example:
Given binary tree {1,#,2,3},

   1
         2
    /
   3

return [1,3,2].

Note: Recursive solution is trivial, could you do it iteratively?

https://leetcode.com/problems/binary-tree-inorder-traversal/

因为js的数组可以放不同类型，放中间的时候放入的是val，两边放入TreeNode对象。

遇到val就直接放入结果中；遇到TreeNode节点，继续按照右中左的顺序入栈。

 1 /**
 2  * Definition for a binary tree node.
 3  * function TreeNode(val) {
 4  *     this.val = val;
 5  *     this.left = this.right = null;
 6  * }
 7  */
 8 /**
 9  * @param {TreeNode} root
10  * @return {number[]}
11  */
12 var inorderTraversal = function(root) {
13     var stack = [], res = [], top;
14     if(root){
15         if(root.right){
16             stack.push(root.right);
17         }
18         stack.push(root.val);
19         if(root.left){
20             stack.push(root.left);
21         }
22     }
23
24     while(stack.length !== 0){
25         top = stack.pop();
26         if(typeof top === "number"){
27             res.push(top);
28         }else{
29             if(top.right){
30                 stack.push(top.right);
31             }
32             stack.push(top.val);
33             if(top.left){
34                 stack.push(top.left);
35             }
36         }
37     }
38     return res;
39 };