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>
#include <stdlib.h> //calloc
#define N 26

int main(void)
{
	int n,i,num=1000000007,ans=1;
	int cnt[N]={0}; //アルファベット配列
	scanf("%d",&n);
	char *s = (char *)calloc(n,sizeof(char));
	scanf("%s",s);
	
	for(i=0;i<n;i++){
		cnt[s[i]-'a']++;
	}
	
	for(i=0;i<N;i++){
		ans *= (cnt[i]+1)%num;
		//printf("%d\n",ans);
	}
	printf("%d\n",ans-1);
	return 0;
}