atcoder#AGC031A. [AGC031A] Colorful Subsequence

[AGC031A] Colorful Subsequence

Score : 200200 points

Problem Statement

You are given a string SS of length NN. Among its subsequences, count the ones such that all characters are different, modulo 109+710^9+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

  • 1N1000001 \leq N \leq 100000
  • SS consists of lowercase English letters.
  • S=N|S|=N

Input

Input is given from Standard Input in the following format:

NN

SS

Output

Print the number of the subsequences such that all characters are different, modulo 109+710^9+7.

4
abcd
15

Since all characters in SS 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 as.

5
abcab
17