binary-tree-preorder-traversal.js

/**
 * Given a binary tree, return the preorder traversal of its nodes' values.
 *
 * For example:
 * Given binary tree {1,#,2,3},
 *    1
 *     \
 *      2
 *     /
 *    3
 * return [1,2,3].
 *
 * Note: Recursive solution is trivial, could you do it iteratively?
 */

/**
 * @param {TreeNode} root
 * @return {number[]}
 */
var preorderTraversal = function(root) {
  if (!root) {
    return [];
  }

  var stack = [root];
  var result = [];

  while (stack.length) {
    var node = stack.pop();
    result.push(node.val);

    if (node.right) {
      stack.push(node.right);
    }
    if (node.left) {
      stack.push(node.left);
    }
  }

  return result;
};

export default preorderTraversal;