Count of total anagram substrings

// C++ program to count total anagram
// substring of a string
#include <bits/stdc++.h>
using namespace std;

// Total number of lowercase characters
#define MAX_CHAR 26

// Utility method to return integer index
// of character 'c'
int toNum(char c)
{
    return (c - 'a');
}

// Returns count of total number of anagram
// substrings of string str
int countOfAnagramSubstring(string str)
{
    int N = str.length();

    // To store counts of substrings with given
    // set of frequencies.
    map<vector<int>, int> mp;

    // loop for starting index of substring
    for (int i=0; i<N; i++)
    {
        vector<int> freq(MAX_CHAR, 0);

        // loop for length of substring
        for (int j=i; j<N; j++)
        {
            // update freq array of current
            // substring
            freq[toNum(str[j])]++;

            // increase count corresponding
            // to this freq array
            mp[freq]++;
        }
    }

    // loop over all different freq array and
    // aggregate substring count
    int result = 0;
    for (auto it=mp.begin(); it!=mp.end(); it++)
    {
        int freq = it->second;
        result += ((freq) * (freq-1))/2;
    }
    return result;
}

//  Driver code to test above methods
int main()
{
    string str = "xyyx";
    cout << countOfAnagramSubstring(str) << endl;
    return 0;
}