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 PHP7 (7.0.15) (judge verdict: Wrong Answer)

<?php
$len = trim(fgets(STDIN)) + 0;
$str = trim(fgets(STDIN));
for($i = 0; $i < $len; $i++){
  $s = $str[$i];
  if(isset($map[$s])){
	  $map[$s]++;
  }else{
	  $map[$s]=2;
  }
}
foreach($map as $num){
  $p *= $num;
  $p = $p  % (1000000000+7);
}
echo $p - 1;