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 Java8 (OpenJDK 1.8.0) (judge verdict: Wrong Answer)

import java.util.Scanner;
public class Main{

    public static void main(String[] args){
        int MOD_NUM = (int)Math.pow(10,9)+7;
        Scanner sc = new Scanner(System.in);

        int[] abc = new int[26];
        for(int i = 0; i < 26; i++)abc[i] = 0;
        int N = sc.nextInt();
        String str = sc.next();

        for(int i = 0; i < N; i++){
            abc[(char)str.charAt(i) - 'a']++;
        }

        long ans = 1;
        for(int i = 0; i < 26; i++){
            ans = (ans  * (abc[i]+1));
        }

        System.out.println((ans - 1)% MOD_NUM);

    }
}