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;
use proconio::marker::Chars;

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

    let alphabet = 26;
    let mut x = vec![0; alphabet];
    let mut y = vec![0; alphabet];

    x[(s[0] as u8 - 'a' as u8) as usize] = 1;
    for i in 1..n {
        y[(s[i] as u8 - 'a' as u8) as usize] += 1;
    }

    let mut maximum = 0;
    for i in 1..n {
        let mut count = 0;
        for j in 0..alphabet {
            if x[j] > 0 && y[j] > 0 {
                count += 1;
            }
        }
        if maximum < count {
            maximum = count;
        }
        x[(s[i] as u8 - 'a' as u8) as usize] += 1;
        y[(s[i] as u8 - 'a' as u8) as usize] -= 1;
    }

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