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: Wrong Answer)

#include <stdio.h>
typedef long long ll;

ll n;
char str[100005];
ll count[30];
ll ans;

int main()
{
	scanf("%lld", &n);
	scanf("%s", str);

	for (ll i = 0; i < n; i++) {
		count[str[i] - 'a']++;
	}

	ans = 1;
	for (ll i = 0; i < 30; i++) {
		if (count[i]) {
			ans = ans * (count[i] + 1);
		}
	}
	ans--;

	printf("%lld\n", ans);

	return 0;
}