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 Rust (1.15.1) (judge verdict: Accepted)

use std::io::stdin;use std::collections::HashMap;fn main() {let mut st = String::new();stdin().read_line(&mut st).unwrap();let _n = st.trim().parse::<usize>().unwrap();let mut st = String::new();stdin().read_line(&mut st).unwrap();let s:Vec<char> = st.trim().chars().collect();let mut map:HashMap<&char, i64> = HashMap::new();for i in &s {let count = map.entry(i).or_insert(1);*count += 1;};let mo = 1000000007;let mut result:i64 = 1;for (_i, j) in map.iter() {result = (result*j)%mo;};println!("{}", result-1)}