find-the-difference.js

// Given two strings s and t which consist of only lowercase letters.
//
// String t is generated by random shuffling string s and then add one more letter at a random position.
//
// Find the letter that was added in t.
//
// Example:
//
// Input:
// s = "abcd"
// t = "abcde"
//
// Output:
// e
//
// Explanation:
// 'e' is the letter that was added.


/**
 * @param {string} s
 * @param {string} t
 * @return {character}
 */
var findTheDifference = function(s, t) {
    const hashMap = {};
    for (var i = 0, l = s.length; i < l; i++) {
        if (!hashMap[s[i]]) {
            hashMap[s[i]] = 1;
        } else {
            hashMap[s[i]]++;
        }
    }
    for (var i = 0, l = t.length; i < l; i++){
        if (!hashMap[t[i]]) {
            return t[i];
        } else {
            hashMap[t[i]]--;
        }
    }
};