[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/

---

树的中序遍历，把节点按照右中左的顺序塞到栈中。

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。

Binary Tree Preorder Traversal:

http://www.cnblogs.com/Liok3187/p/4805834.html

Binary Tree Postorder Traversal：

http://www.cnblogs.com/Liok3187/p/4822303.html

/**
 * Definition for a binary tree node.
 * function TreeNode(val) {
 *     this.val = val;
 *     this.left = this.right = null;
 * }
 */
/**
 * @param {TreeNode} root
 * @return {number[]}
 */
var inorderTraversal = function(root) {
    var stack = [], res = [], top;
    if(root){
        stack.push(root);
    }

    while(stack.length !== 0){
        top = stack.pop();
        if(typeof top === "number"){
            res.push(top);
        }else{
            if(top.right){
                stack.push(top.right);
            }
            stack.push(top.val);
            if(top.left){
                stack.push(top.left);
            }
        }
    }
    return res;
};