https://leetcode.com/problems/valid-anagram/

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 a different word or phrase, typically using all the original letters exactly once.

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.

Idea:

Frequency counter

Solution:

class Solution {
public:
    static const int NUM_LETTERS = 26;

    bool isAnagram(string s, string t) {
        int arr[NUM_LETTERS] = {0};

        if (s.size() != t.size()) {
            return false;
        }

        for(int i = 0; i < s.size(); ++i) {
            arr[s[i] - 'a']++;
            arr[t[i] - 'a']--;
        }

        for(int i = 0; i < NUM_LETTERS; ++i) {
            if(arr[i] != 0) {
                return false;
            }
        }

        return true;
    }
};

Complexity Analysis:

Time

O(N + M) + constant time

Memory

O(1) array fixed to 26