0814-binary-tree-pruning.js

/**
 * 814. Binary Tree Pruning
 * https://leetcode.com/problems/binary-tree-pruning/
 * Difficulty: Medium
 *
 * Given the root of a binary tree, return the same tree where every subtree (of the given tree)
 * not containing a 1 has been removed.
 *
 * A subtree of a node node is node plus every node that is a descendant of node.
 */

/**
 * 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 {TreeNode}
 */
var pruneTree = function(root) {
  if (!root) return null;
  root.left = pruneTree(root.left);
  root.right = pruneTree(root.right);
  if (!root.left && !root.right && root.val === 0) {
    return null;
  }
  return root;
};