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 Java8 (OpenJDK 1.8.0) (judge verdict: Accepted)

import java.lang.reflect.Array;
import java.util.*;

public class Main {

    public static void main(String[] args) {

        Scanner sc = new Scanner(System.in);
        int ans= 0;
        int n = sc.nextInt();
        char[] c  = sc.next().toCharArray();

        for(int i=1;i<n;i++){
            int temp = 0;
            HashSet<Character> alphabet = new HashSet<>();
            for(int j=0;j<i;j++)alphabet.add(c[j]);
            for(int j=i;j<n;j++){
                if(alphabet.contains(c[j])){
                    temp++;
                    alphabet.remove(c[j]);
                }
            }
            ans = Math.max(ans,temp);
        }

        System.out.println(ans);

    }
}