Valid Anagram

Given two strings s and t, return true if the two strings are anagrams of each other, otherwise return false.

An anagram is a string that contains the exact same characters as another string, but the order of the characters can be different.

Approach

If the strings have different lengths, they cannot be anagrams. Otherwise, count character frequencies using a 26-length array for lowercase letters, incrementing for s and decrementing for t. If all counts return to zero, the strings are anagrams. This handles the empty-string case and repeated characters directly.

Why It Works

Each position in the count array tracks the net difference between occurrences of a character in s and t. If the strings are anagrams, every character appears the same number of times, so all net differences are zero. Any mismatch leaves a non-zero count, correctly returning false.

Complexity

• Time: O(n)
• Space: O(1)

Reference Implementation (Python)

class Solution:
    def isAnagram(self, s: str, t: str) -> bool:
        if len(s) != len(t):
            return False
        counts = [0] * 26
        for i in range(len(s)):
            counts[ord(s[i]) - ord('a')] += 1
            counts[ord(t[i]) - ord('a')] -= 1
        return all(count == 0 for count in counts)