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 <iostream>
# include <cstring>
using namespace std;

int N;
string S;
long long counting[100005];
long long ans=1;
int order;

int main()
{
    cin>>N;
    cin>>S;

    for (int i=0; i<N; i++)
    {
        order=S[i]-'a';
        counting[order]++;
    }

    for (int i=0; i<N; i++)
    {
        if (counting[i]>0)
        {
            ans=(ans*((counting[i]+1)%1000000007))%1000000007;
        }
    }

    ans=(ans-1)%100000000;

    cout<<ans<<endl;
}