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)

// -*- coding:utf-8-unix -*-

use proconio::input;

fn main() {
    input! {
        n: usize,
        s: String,
    }

    let vc: Vec<char> = s.chars().collect();
    let mut vx = vec![0; 26];
    let mut vy = vec![0; 26];
    for c in &vc {
        vy[(*c as u8 - b'a') as usize] += 1;
    }

    let mut ans = 0;
    for i in 0..n {
        vx[(vc[i] as u8 - b'a') as usize] += 1;
        vy[(vc[i] as u8 - b'a') as usize] -= 1;

        let mut current = 0;
        for j in 0..26 {
            if vx[j] * vy[j] > 0 {
                current += 1;
            }
        }
        ans = ans.max(current);
    }
    println!("{}", ans);
}