#144 - Binary Tree Preorder Traversal

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Problem Description

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

Solution

/**
 * 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) {
  return root
    ? [root.val, ...preorderTraversal(root.left), ...preorderTraversal(root.right)]
    : [];
};