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 Java (OpenJDK 11.0.6) (judge verdict: Accepted)

import java.util.*;
 
public class Main {
    public static void main(String[] args) throws Exception {
        Scanner sc = new Scanner(System.in);
        int num = sc.nextInt();
        String str0 = sc.next();
        int max = 0;
        for(int i = 0; i < num; i++){
        	String str1 = str0.substring(0,i);
            String str2 = str0.substring(i);
            int count = 0;
            ArrayList<String> list = new ArrayList<>();
            for(int x = 0; x < i; x++){
            	if(str2.contains(str1.substring(x, x + 1)) && list.contains(str1.substring(x, x + 1)) == false){
                	list.add(str1.substring(x, x + 1));
                    count++;
                }
                if(max < count){
                	max = count;
                }
            }
        }
        System.out.println(max); 
    }
}