Valid Anagram

Problem

Given two strings s and t, return true if t is an anagram of s, and false otherwise.

An Anagram is a word or phrase formed by rearranging the letters of a different word or phrase, typically using all the original letters exactly once.

 

Example 1:

Input: s = "anagram", t = "nagaram"
Output: true

Example 2:

Input: s = "rat", t = "car"
Output: false

 

Constraints:

• 1 <= s.length, t.length <= 5 * 104
• s and t consist of lowercase English letters.

Solution

/**
 * @param {string} s
 * @param {string} t
 * @return {boolean}
 */
var isAnagram = function(s, t) {
    if (s.length !== t.length) {
        return false;
    }

    const map = {};
    for (let i = 0; i < s.length; i++) {
        const c1 = s[i];
        const c2 = t[i];
        if (!(c1 in map)) {
            map[c1] = 0;
        }
        if (!(c2 in map)) {
            map[c2] = 0;
        }
        map[c1]++;
        map[c2]--;
    }
    return Object.values(map).every(n => !n);
};

Use a hashmap map to keep track the number of times a character appears in s and t. More specifically, we add 1 if it appears in s, and subtract 1 if it appears in t. Thus, if every value in map is 0, s must be an anagram of t.