144.binary-tree-preorder-traversal.js

/*
 * @lc app=leetcode id=144 lang=javascript
 *
 * [144] Binary Tree Preorder Traversal
 */

// @lc code=start
/**
 * Definition for a binary tree node.
 * function TreeNode(val, left, right) {
 *     this.val = (val===undefined ? 0 : val)
 *     this.left = (left===undefined ? null : left)
 *     this.right = (right===undefined ? null : right)
 * }
 */
/**
 * @param {TreeNode} root
 * @return {number[]}
 */
var preorderTraversal = function(root) {
    var stack = [];
    var result = [];
    if (root != null) {
        stack.push(root);
    }
    while (stack.length > 0) {
        var node = stack.pop();
        result.push(node.val);
        if (node.right != null) {
            stack.push(node.right);
        }
        if (node.left != null) {
            stack.push(node.left);
        }
    }
    return result;
};
// @lc code=end