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 proconio::{input, fastout};
use proconio::marker::{Chars};
use proconio::marker::Usize1;
use std::cmp::*;

macro_rules! debug {
      ($($a:expr),*) => {
          eprintln!(concat!($(stringify!($a), " = {:?}, "),*), $($a),*);
      }
  }

#[fastout]
fn main() {
    input!{
        n: usize,
        s: Chars,
    }

    let mut ans = 0;
    for cut in 1..n {
        let mut alpha_front: Vec<usize> = vec![0;30];
        let mut alpha_back: Vec<usize> = vec![0;30];
        let mut cnt = 0;
        for i in 0..cut {
            alpha_front[(s[i] as usize) - ('a' as usize)] += 1;
        }
        for i in cut..n {
            alpha_back[(s[i] as usize) - ('a' as usize)] += 1;
        }
        for i in 0..30 {
            if alpha_front[i]!=0 && alpha_back[i]!=0 {
                cnt += 1;
            }
        }
        debug!(alpha_front);
        ans = max(ans, cnt);

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