Problem:
Score : 200 points

Problem Statement

You are given a string S of length N consisting of lowercase English letters.
We will cut this string at one position into two strings X and Y.
Here, we would like to maximize the number of different letters contained in both X and Y.
Find the largest possible number of different letters contained in both X and Y when we cut the string at the optimal position.

Constraints

2 \leq N \leq 100

|S| = N

S consists of lowercase English letters.

Input

Input is given from Standard Input in the following format:

N
S

Output

Print the largest possible number of different letters contained in both X and Y.

Sample Input 1

6
aabbca

Sample Output 1

2

If we cut the string between the third and fourth letters into X = aab and Y = bca, the letters contained in both X and Y are a and b.
There will never be three or more different letters contained in both X and Y, so the answer is 2.

Sample Input 2

10
aaaaaaaaaa

Sample Output 2

1

However we divide S, only a will be contained in both X and Y.

Sample Input 3

45
tgxgdqkyjzhyputjjtllptdfxocrylqfqjynmfbfucbir

Sample Output 3

9

Solution in Rust (1.42.0) (judge verdict: Accepted)

use std::cmp::max;
use std::io::stdin;

fn main() {
    let mut is = String::new();
    stdin().read_line(&mut is).ok();
    is.clear();
    stdin().read_line(&mut is).ok();
    let s = is.trim();
    let mut ans = 0;

    for i in 1..s.len() {
        let (x, y) = s.split_at(i);
        let mut x_cnt = [false; 26];
        let mut y_cnt = [false; 26];

        x.chars().for_each(|c| x_cnt[c as usize - 0x61] = true);
        y.chars().for_each(|c| y_cnt[c as usize - 0x61] = true);
        ans = max(
            ans,
            x_cnt
                .iter()
                .zip(y_cnt.iter())
                .filter(|e| *e.0 && *e.1)
                .count(),
        );
    }

    println!("{}", ans);
}