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 <stdint.h>


int main(void) {
  int N;
  scanf("%d", &N);

  int S_NUM[26];
  for(int i = 0; i < 26; i++) {
    S_NUM[i] = 0;
  }

  char S[100000];
  scanf("%s", S);
  for(int i = 0; i < N; i++) {
    S_NUM[S[i] - 'a']++;
  }

  uint64_t SUM = 1;
  for(int i = 0; i < 26; i++) {
    SUM *= (S_NUM[i] + 1);
  }
  SUM--;

  uint64_t mod = SUM % (1000000000+7);
  printf("%ld\n", mod);

  return 0;
}