242 Valid Anagram

Given two strings s and t, write a function to determine if t is an anagram of s.

For example, s = "anagram", t = "nagaram", return true. s = "rat", t = "car", return false.

Solution
O(N) time, O(1) space

class Solution {
public:
    bool isAnagram(string s, string t) {
        int prime[26] = {2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97, 101};
        int sum = 0;
        int ns = s.size(), nt = t.size();
        for ( int i = 0; i <= ns-1; i++ ) {
            int j = s[i] - 'a';
            sum += prime[j] * (j+1);
        }
        for ( int i = 0; i <= nt-1; i++ ) {
            int j = t[i] - 'a';
            sum -= prime[j] * (j+1);
        }
        return ( sum == 0 );
    }
};

O(N) time, O(N) space

class Solution {
public:
    bool isAnagram(string s, string t) {
        unordered_map<char, int> map;
        int ns = s.size(), nt = t.size();
        if ( ns != nt ) return false;
        for ( int i = 0; i <= ns-1; i++ ) {
            if ( map.find(s[i]) == map.end() ) map[s[i]] = 1;
            else map[s[i]] += 1;
        }
        for ( int i = 0; i <= nt-1; i++ ) {
            if ( map.find(t[i]) == map.end() ) return false;
            map[t[i]] -= 1;
            if ( map[t[i]] == -1 ) return false;
        }
        return true;
    }
};