Valid Anagram

Problem

Given two strings s and t, return true if t is an anagram of s (same letters, possibly different order).

Constraints

• 1 ≤ s.length, t.length ≤ 5·10⁴
• s and t consist of lowercase English letters

Approach — Hashing & Counting

This is a Hashing & Counting problem. The idea: store what you've seen in a hash map for O(1) lookups, trading a little space to avoid a nested scan. Work through the reference code below line by line, then re-derive it yourself in the editor — that's how the pattern sticks.

Complexity: O(n) time, O(n) space.

Solution code

Python

class Solution:
    def isAnagram(self, s, t):
        from collections import Counter
        return Counter(s) == Counter(t)

Java

class Solution {
    public boolean isAnagram(String s, String t) {
        if (s.length() != t.length()) {
            return false;
        }
        int[] counts = new int[26];
        for (int i = 0; i < s.length(); i++) {
            counts[s.charAt(i) - 'a']++;
            counts[t.charAt(i) - 'a']--;
        }
        for (int count : counts) {
            if (count != 0) {
                return false;
            }
        }
        return true;
    }
}

Practice it

Reading a solution isn't the same as being able to write it under pressure. Open this problem in the in-browser editor, hide the solution, and solve it from scratch — your code runs against real test cases instantly.