0623-add-one-row-to-tree.js

/**
 * 623. Add One Row to Tree
 * https://leetcode.com/problems/add-one-row-to-tree/
 * Difficulty: Medium
 *
 * Given the root of a binary tree and two integers val and depth, add a row of nodes with value
 * val at the given depth depth.
 *
 * Note that the root node is at depth 1.
 *
 * The adding rule is:
 * - Given the integer depth, for each not null tree node cur at the depth depth - 1, create two
 *   tree nodes with value val as cur's left subtree root and right subtree root.
 * - cur's original left subtree should be the left subtree of the new left subtree root.
 * - cur's original right subtree should be the right subtree of the new right subtree root.
 * - If depth == 1 that means there is no depth depth - 1 at all, then create a tree node with
 *   value val as the new root of the whole original tree, and the original tree is the new root's
 *   left subtree.
 */

/**
 * 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
 * @param {number} val
 * @param {number} depth
 * @return {TreeNode}
 */
var addOneRow = function(root, val, depth) {
  if (depth === 1) {
    return new TreeNode(val, root);
  }
  dfs(root, 1);

  return root;

  function dfs(node, level) {
    if (!node) return;
    if (level === depth - 1) {
      node.left = new TreeNode(val, node.left);
      node.right = new TreeNode(val, null, node.right);
      return;
    }
    dfs(node.left, level + 1);
    dfs(node.right, level + 1);
  }
};