[LeetCode][JavaScript]Binary Tree Postorder Traversal

Binary Tree Postorder Traversal

Given a binary tree, return the postorder traversal of its nodes' values.

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

   1
    
     2
    /
   3

return [3,2,1].

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

---

同样的配方，同样的味道。

Binary Tree Inorder Traversal:

http://www.cnblogs.com/Liok3187/p/4808974.html

Binary Tree Preorder Traversal:

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

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