242. Valid Anagram

At a Glance

• Topic: String
• Pattern: Hash Map
• Difficulty: Easy
• LeetCode: 242

Problem Statement

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

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.

Follow up: What if the inputs contain Unicode characters? How would you adapt your solution to such a case?

Approach & Solution Steps

Use an array or hash map to count the frequencies of characters in the first string, then decrement the frequencies for the second string. If all frequencies are zero, they are anagrams.

Optimal JS Solution

function isAnagram(s, t) {
  if (s.length !== t.length) return false;
  const counts = new Array(26).fill(0);
  for (let i = 0; i < s.length; i++) {
    counts[s.charCodeAt(i) - 97]++;
    counts[t.charCodeAt(i) - 97]--;
  }
  return counts.every(count => count === 0);
}

Edge Cases & Pitfalls

• Always consider empty or null inputs.
• Watch out for off-by-one index errors.