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)

#![allow(unused_imports)]

use text_io::*;
use proconio::*;
use std::collections::*;
use std::process::exit;
use std::cmp::*;
use itertools::Itertools;

fn main() {
    let a: usize = read!();
    let b: String = read!();
    let b = b.chars().collect_vec();
    let mut sum:usize = 0;
    let mut ans:usize = 0;
    let mut c:usize = 0;
    let mut d:usize = 0;
    for i in 0..b.len() {
        for j in 0..i {
            if b[i]==b[j] {
               c=1;
            }
        }
        for j in i+1..b.len() {
            if b[i]==b[j] {
               d=1;
            }
        }
        sum=sum-c+d;
        c=0;
        d=0;
        if ans<sum {
            ans=sum;
        }
    }
    println!("{}",ans)
}