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 (1.15.1) (judge verdict: Accepted)

use std::io;

fn main() {
    let mut n = String::new();
    io::stdin().read_line(&mut n).unwrap();
    let n: u32 = n.trim().parse().unwrap();

    let mut s = String::new();
    io::stdin().read_line(&mut s).unwrap();

    let vec: Vec<_> = s.trim().chars().collect();
    let mut max = 0;

    for i in 1..n {
        let mut cnt = 0;
        let mut exist = Vec::with_capacity(32);
        for j in 0..i {
            if exist.contains(&vec[j as usize]) {
                continue;
            }
            for k in i..n {
                if vec[j as usize] == vec[k as usize] {
                    cnt += 1;
                    exist.push(vec[j as usize]);
                    break;
                }
            }
        }

        if cnt > max {
            max = cnt;
        }
    }
    println!("{}", max);
}