Overview

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 another, using all the original letters exactly once.

Implement isAnagram(s, t).

Constraints

• 1 ≤ s.length, t.length ≤ 50000
• s and t consist of lowercase English letters only.
• Aim for $O(n)$ time, $O(1)$ space (the char frequency map has at most 26 entries).

Examples

isAnagram("anagram", "nagaram");
// → true

isAnagram("rat", "car");
// → false

isAnagram("listen", "silent");
// → true

Notes

• If lengths differ, immediately return false.
• Count character frequencies for s, then decrement for t. If any count goes below 0, return false.
• Alternatively, count both and compare.

Solution

function isAnagram(s, t) {
  if (s.length !== t.length) return false;

  const counts = new Array(26).fill(0);
  const aCode = 'a'.charCodeAt(0);

  for (let i = 0; i < s.length; i++) {
    counts[s.charCodeAt(i) - aCode]++;
    counts[t.charCodeAt(i) - aCode]--;
  }

  return counts.every(c => c === 0);
}

Resources

• Valid Anagram — LeetCode
• Anagram — Wikipedia