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::cmp;
use std::io::Read;

fn main() {
    let mut buff = String::new();
    std::io::stdin().read_to_string(&mut buff).unwrap();
    let mut iter = buff.split_whitespace();

    let _n: i32 = iter.next().unwrap().parse().unwrap();
    let s: String = iter.next().unwrap().parse().unwrap();

    let mut mx: i32 = 0;
    for i in 1..s.len() {
        let t = &s[0..i];
        let u = &s[i..s.len()];
        let mut cnt: i32 = 0;
        for c in ('a' as u8)..('z' as u8 + 1) {
            if t.contains(c as char) && u.contains(c as char) {
                cnt = cnt + 1;
            }
            mx = cmp::max(mx, cnt);
        }
    }
    println!("{}", mx);

    ()
}