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 <bits/stdc++.h>

using namespace std;
#define rep(i,n) for(int i=0;i<n;i++)
typedef long long ll;

int main(){
    ll n;
    cin >> n;
    string s;
    cin >> s;
    map<char,ll> mp;
    rep(i,n){
        mp[s[i]]++;
    }
    ll ans=1;
    rep(i,n){
        if(mp[s[i]]!=0)ans=ans*(mp[s[i]]+1);
        mp[s[i]]=0;
    }
    ll a=pow(10,9)+7;
    
    cout << (ans-1)%a;
}