Skip to content
Optimal Lab

Arrays & Hashing · 051Easy

Valid Anagram

Given two strings s and t, return true if t is an anagram of s. An anagram uses exactly the same characters with the same counts, reordered.

Constraints

  • 1 <= s.length, t.length <= 5 * 10^4
  • s and t consist of lowercase English letters.

Examples

isAnagram("anagram", "nagaram")  ->  true
isAnagram("rat", "car")          ->  false
isAnagram("a", "ab")             ->  false   // different lengths
isAnagram("a", "a")              ->  true   // shortest possible input
isAnagram("ab", "ba")            ->  true   // pure reordering
isAnagram("aacc", "ccac")        ->  false   // same letter set, different counts

Edge cases

  • Character COUNTS must match, not just the set of characters.
  • FOLLOW-UP
  • Follow-up: what changes for Unicode input?
Show the target complexity (spoiler)
Naive
O(n log n) time — sort both strings and compare.
Target
O(n) time, O(1) space — a 26-slot count array incremented by s and decremented by t.

Solve it

By hand, in your editor. The runner checks answers and timing.

git clone https://github.com/sarmadkung/optimal-round
cd optimal-round
# open problems/01-arrays-hashing/051-valid-anagram.js
./practice c 051
Open the file on GitHub ↗

Stuck? Watch the pattern run

Interactive sessionHash map: group anagrams →Interactive sessionTwo Sum, three ways →