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::collections::HashSet;
use whiteread::parse_line;

fn main() {
    let _n: usize = parse_line().unwrap();
    let s: String = parse_line().unwrap();
    let s: Vec<u8> = s.into_bytes();
    let mut setl: HashSet<u8> = HashSet::new();
    let mut setr: HashSet<u8> = HashSet::new();
    let mut ans = 0;

    for i in 1..s.len() - 1 {
        setl.clear();
        setr.clear();
        for &c in &s[..i] {
            setl.insert(c);
        }
        for &c in &s[i..] {
            setr.insert(c);
        }
        ans = ans.max(setl.intersection(&setr).count());
    }
    println!("{}", ans);
}