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::*;
use std::str::FromStr;

fn read<T: FromStr>() -> T {
    let stdin = stdin();
    let stdin = stdin.lock();
    let token: String = stdin
        .bytes()
        .map(|c| c.expect("failed to read char") as char)
        .skip_while(|c| c.is_whitespace())
        .take_while(|c| !c.is_whitespace())
        .collect();
    token.parse().ok().expect("failed to parse token")
}

use std::vec::*;
use std::cmp::*;
use std::iter::*;

fn main() {
    let n: u32 = read();

    let mut s0: String = read();
    let mut s: Vec<char> = Vec::new();

    for i in 0..n {
        let c = s0.pop().expect("");
        s.push(c);
    }

    let mut k = 0;
    for i in 1..n {
        let mut ki = 0;
        let (x, y) = s.split_at(i as usize);
        let mut xs = x.to_vec();
        let mut ys = y.to_vec();
        xs.sort();
        xs.dedup();
        ys.sort();
        ys.dedup();
        while xs.len() > 0 && ys.len() > 0 {
            if xs[0] == ys[0] {
                ki += 1;
                xs.remove(0);
                ys.remove(0);
            }
            else if xs[0] < ys[0] {
                xs.remove(0);
            }
            else {
                ys.remove(0);
            }
        }
        for j in 0..xs.len() {
            // print!("{}{} ", xs[j], ys[j]);
            if ys.len() <= j {break}
            if xs[j] == ys[j] {
                ki += 1;
            }
            else {
                break
            }
        }
        k = max(k, ki);
    }

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