solutions/0389-find-the-difference.js

/**
 * 389. Find the Difference
 * https://leetcode.com/problems/find-the-difference/
 * Difficulty: Easy
 *
 * You are given two strings s and t.
 *
 * String t is generated by random shuffling string s and then add one more letter at
 * a random position.
 *
 * Return the letter that was added to t.
 */

/**
 * @param {string} s
 * @param {string} t
 * @return {character}
 */
var findTheDifference = function(s, t) {
  const map = new Map();
  t.split('').forEach(c => map.set(c, (map.get(c) ?? 0) + 1));
  s.split('').forEach(c => map.set(c, map.get(c) - 1));
  return Array.from(map).find(([letter, count]) => count)[0];
};