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;

int MOD = 1e+7;

int main() {
	#if LOCAL
	freopen("a.in", "r", stdin);
	#endif

	int N;
	string t;
	int cnt[26]={0};
	cin>>N>>t;
	for(int i=0;i<N;i++) {
		cnt[t[i]-'a']++;
	}
	long long res = 1;
	for(int i=0;i<26;i++) {
		res*=(long long)(cnt[i]+1);
		res%=MOD;
	}
	res-=1;
	cout<<res<<endl;
	return 0;
}