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 <vector>
#include <string>
#include <bitset>
#include <cmath>
#include <iomanip>
#include <stack>
#include <set>
#include <queue>
#include <algorithm>
#include <deque>
using namespace std;

#define INF 1e18
#define int long long
#define MOD 1000000007

signed main() {
    int n; cin >> n;
    string s; cin >> s;
    vector<int> cnt(26, 0);

    for(int i = 0; i < n; i++) {
        cnt[s[i] - 'a']++;
    }

    int ans = 1;
    for(int i = 0; i < 26; i++) {
        if(cnt[i] > 0) {
            ans *= (cnt[i] + 1);
        }
    }

    cout << (ans - 1) % MOD << endl;
    return 0;
}