postorderTraversal

postorderTraversal.js

/**
 * 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 = root ? [root] : [];
    var prev = null;
    var res = [];
    while(stack.length > 0) {
        var node = stack.pop();
        var visit = node;
        
        if(!node.left) {
            visit = prev === node.right ? node : node.right;
        }
        else if(!prev || prev !== node.right){
            visit = prev === node.left ? node.right : node.left;
        }
        
        if(visit && visit !== node) {
            stack.push(node);
            stack.push(visit);
        }
        else {
            res.push(node.val);
        }
        
        prev = node;
    }
    
    return res;
};