LeetCode 242. Valid Anagram

class Solution {
public:
    bool isAnagram(string s, string t) {
        if(s.size()!=t.size())
            return false;
        if(s.size()==0)
            return true;
        
        int n = s.size();
        unordered_map<char,int> res;
        for(int i = 0;i < n ;i++){
            res[s[i]]++;
        }
        for(int i =0;i<n ;i++){
            if( res[t[i]] <= 0 )
                return false;
            else
                res[t[i]]--;
        }
        return true;
    }
};