Problem:
Score : 200 points

Problem Statement

You are given a string S of length N.
Among its subsequences, count the ones such that all characters are different, modulo 10^9+7. Two subsequences are considered different if their characters come from different positions in the string, even if they are the same as strings.

Here, a subsequence of a string is a concatenation of one or more characters from the string without changing the order.

Constraints

1 \leq N \leq 100000

S consists of lowercase English letters.

|S|=N

Input

Input is given from Standard Input in the following format:

N
S

Output

Print the number of the subsequences such that all characters are different, modulo 10^9+7.

Sample Input 1

4
abcd

Sample Output 1

15

Since all characters in S itself are different, all its subsequences satisfy the condition.

Sample Input 2

3
baa

Sample Output 2

5

The answer is five: b, two occurrences of a, two occurrences of ba. Note that we do not count baa, since it contains two as.

Sample Input 3

5
abcab

Sample Output 3

17

Solution in C++14 (GCC 5.4.1) (judge verdict: Wrong Answer)

#include <stdio.h>
#include <iostream>
#include <vector>
#include <string>
#include <map>
#define MOD 1000000007

using namespace std;
typedef long long ll;

int main(){
  	int N;
	string S;
  	cin >> N;
  	cin >> S;
  	vector<int> multi;
  	int count = 0;
  	ll ans = 1;
	map<char, int> m;
    for(int i = 0; i < N; i++){
    	m[S[i]]++;
    }
  	for(auto x: m){
    	ans *= (x.second+1);
    }
  	if(N == 0) ans = 0;
  	else ans -= 1;
  	cout << ans << endl;
}