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# (Mono 4.6.2.0) (judge verdict: Wrong Answer)

using System;
using System.Linq;
public class c
{
  public static void Main()
  {
    int n = int.Parse(Console.ReadLine());
    string s= Console.ReadLine();
    string ABC = "abcdefghijklmnopqrstuvwxyz";
    char[] abc=ABC.ToCharArray();
    int[] count = new int[26];
    int ans =0;
    for(int i=0;i<n;i++)
    {
        for(int j=0;j<26;j++)
        {
            if(s[i]==abc[j])count[j]++;
        }
    }
    for(int i=0;i<26;i++)
    {
        if(count[i]!=0)ans++;
    }
    Console.WriteLine(ans);
  }
}