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>

int main(void){
    static char str[100001];
    unsigned long long int count = 1;
    int len;//文字列の長さ
    int i;
    
    int bucket[26] = {0};
    
    scanf("%d", &len);
    scanf("%s", str);
    
    for(i = 0; i < len; i++){
        bucket[str[i] - 'a']++;
    }
    
    for(i = 0; i < 26; i++){
        if(bucket[i]){
            count *= (bucket[i] + 1);
        }
    }
    
    printf("%llu\n", (count-1) % 1000000007);
    
    return 0;
}