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: Runtime Error)

#include<stdio.h>
#include<string.h>
void aaa(int a){
  int M=1;
  int i;
  for(i=0;i<a;i++){
    M=M*2;
  }
  M=M-1;
  
  int L;
  L=1;					/*剰余*/
  for(i=0;i<10;i++){
    L=L*10;
  }
  L=L+7;
  int k;
  k=M%L;
  printf("%d\n",k);
}

int main(void){
  int i,j,N,M,X,L;
  char S[N];
  int cout=0;
  
  scanf("%d",&N);
  scanf("%s",S);
  //printf("%d\n",N);
  //printf("%s\n",S);
  M=1;
  
  //printf("%d\n",M);
  
  

  int c=0;
  int h;
  for(i=0;i<N;i++){
    for(j=0;j<N;j++){
      if(S[i]==S[j]){
        //printf("efe");
        c++;
      }
    }
    if(i==N-1&&j==N){
		h=c;
      aaa(h);
    }
  }


  for(i=0;i<h;i++){
    M=M*2;
  }
  M=M-1;
  
  
  L=1;					/*剰余*/
  for(i=0;i<10;i++){
    L=L*10;
  }
  L=L+7;
  int k;
  k=M%L;
  //printf("%d\n",k);
  
  
  return 0;
}