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 (GCC 5.4.1) (judge verdict: Accepted)

/*
	submission # - User: herp_sy
	https://atcoder.jp/contests/

	coding: utf-8
	lang: C (GCC 5.4.1)
*/

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>
#include <stdbool.h>

#define _CRT_SECURE_NO_WARNINGS
#define TLong long long
#define TBMod 1000000007

int main(int argc, char const *argv[])
{
	int n;
	char s[100003];
	TLong ans = 1, charcnt[26] = { 0 };

	scanf("%d", &n);
	scanf("%s", s);

 	for(int i = 0; i < n; ++i)	++charcnt[s[i] - 'a'];
 	for(int i = 0; i < 26; ++i) ans = (TLong)ans * (charcnt[i] + 1) % TBMod;
 	printf("%lld\n", (ans + TBMod - 1) % TBMod);
}