0094-binary-tree-inorder-traversal.js

/**
 * 94. Binary Tree Inorder Traversal
 * https://leetcode.com/problems/binary-tree-inorder-traversal/
 * Difficulty: Easy
 *
 * Given the root of a binary tree, return the inorder traversal of its nodes' values.
 */

/**
 * 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 inorderTraversal = function(root) {
  const result = [];
  const stack = [];

  while (root || stack.length) {
    if (root) {
      stack.push(root);
      root = root.left;
    } else {
      const { val, right } = stack.pop();
      result.push(val);
      root = right;
    }
  }

  return result;
};