#652 - Find Duplicate Subtrees

Medium • View on LeetCode • View on GitHub

Problem Description

Given the root of a binary tree, return all duplicate subtrees.

For each kind of duplicate subtrees, you only need to return the root node of any one of them.

Two trees are duplicate if they have the same structure with the same node 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 {TreeNode[]}
 */
var findDuplicateSubtrees = function(root) {
  const map = new Map();
  const result = [];

  serialize(root);

  return result;

  function serialize(node) {
    if (!node) return '#';
    const key = `${node.val},${serialize(node.left)},${serialize(node.right)}`;
    map.set(key, (map.get(key) || 0) + 1);
    if (map.get(key) === 2) {
      result.push(node);
    }
    return key;
  }
};