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>

#define MOD 1000000007

int mod_multi(int a,int b){
    long long int ret;
    ret = a*b;
    if(ret>MOD)ret %= MOD;
    return ret;
}

int main(void){
    int n;
    scanf("%d",&n);
    char str[n];
    scanf("%s",str);
    int ans = 1;
    int cc[26] = {};
    for(int i = 0;i < n;i++)cc[str[i]-'a']++;
    for(int i = 0;i < 26;i++)ans = mod_multi(ans,cc[i]+1);
    printf("%d",ans-1);
    return 0;
}