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)

//
// Created on 2019-02-09.
//
#include "bits/stdc++.h"
using namespace std;
typedef long long ll;
template<class T> bool INRANGE(T x,T a,T b) { return a<=x&&x<=b; }

#define REP(i,n) for(int i=0;i<(n);++i)
#define ALL(v) (v).begin(),(v).end()
#define RALL(a) (a).rbegin(), (a).rend()
#define debug(x) cerr << #x << " = " << (x) << " (L" << __LINE__ << ")" \
                      << " " << __FILE__ << endl;

#define PB push_back
#define INF 1e9
#define MOD (ll)1e9+7
#define EPS 1e-9

typedef vector<int> vi;
typedef vector<string> vs;
typedef vector<vi> vvi;
typedef pair<int, int> pii;


int main()
{
    cin.tie(0);
    ios::sync_with_stdio(false);

    int n;
    string s;
    bool is_contain_same = false;
    cin >> n >> s;

    ll ans = -1;

    for (int bit = 0; bit < (1<<n); ++bit)
    {

        is_contain_same = false;
        vector<char> S;
        for (int i = 0; i < n; ++i) {
            if (bit & (1<<i)) { // i が bit に入るかどうか
                for (char ch : S) if (s[i] == ch) is_contain_same = true;
                if (!is_contain_same) S.emplace_back(s[i]);
            }
        }

        if (!is_contain_same) ans++;
        if (ans >= MOD) ans -= MOD;

    }

    cout << ans << endl;


    return 0;

}