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;

fn main(){
    getline();
    let buf = getline();
    let str = buf.trim();
    let mut cnt1 = [0; 30];
    let mut cnt2 = [0; 30];
    let mut best = 0;
    
    for e in str.bytes() {
        cnt1[e as usize - 'a' as usize] += 1;
    }
    
    for e in str.bytes() {
        let i = e as usize - 'a' as usize;
        cnt1[i] -= 1;
        cnt2[i] += 1;
        let mut c = 0;
        for j in 0..30 {
            c += if (cnt1[j] * cnt2[j] > 0){1}else{0};
        }
        best = cmp::max(best, c);
    }
    println!("{}", best);
}

fn getline() -> String{
    let mut r = String::new();
    std::io::stdin().read_line(&mut r).ok();
    return r;
}