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)

#include<stdio.h>
#include<stdlib.h>
#include<math.h>
#include<string.h>
#include <time.h>
typedef long long ll;
typedef long double ld;
#define INF (1LL<<60)
#define MOD1 1000000007
/*swap 交換*/
void swap(ll *a, ll *b){ll c;c=*b;*b=*a;*a=c;}
/*2つのうち大きい数を返す*/
ll max2(ll a,ll b){return a>=b?a:b;}
/*2つのうち小さい数を返す*/
ll min2(ll a,ll b){return a>=b?b:a;}
/*絶対値*/
ll ABS(ll a){return a>=0?a:(-a);}
typedef struct{
    ll aa;
    ll bb;
}frequent;
// 小大
int compare(const void *a, const void *b){return *(ll *)a - *(ll *)b;}

int main(void){
    ll n,i,ans=1;
    scanf("%lld",&n);
    char s[n+5];
    scanf("%s",s);
    ll letter[26];
    for(i=0;i<26;i++){
        letter[i]=0;
    }
    // ll a;
    for(i=0;i<n;i++){
        // a = (ll)s[i];
        letter[(ll)s[i] -97]++;
    }
    for(i=0;i<26;i++){
        ans*=letter[i]+1;
        ans%=MOD1;
    }
    printf("%lld\n",ans-1);
    return 0;
}