Contest: Task: Related: TaskB

Score : $200$ points

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.

- $1 \leq N \leq 100000$
- $S$ consists of lowercase English letters.
- $|S|=N$

Input is given from Standard Input in the following format:

$N$ $S$

Print the number of the subsequences such that all characters are different, modulo $10^9+7$.

4 abcd

15

Since all characters in $S$ itself are different, all its subsequences satisfy the condition.

3 baa

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 `a`

s.

5 abcab

17