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.util.Arrays;
import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        String s = sc.next();
        int count = 0;
        int[] ans = new int[n - 1];
        String x;
        String y;
        for (int i = 1; i < n; i++) {

            x = s.substring(0, i);

            y = s.substring(i);

            for (int j = 0; j < x.length(); j++) {
                if (y.contains(String.valueOf(x.charAt(j)))) {
                    if (j == 0) {

                        count++;
                    } else if (!(x.substring(0, j).contains(String.valueOf(x.charAt(j))))) {
                        count++;

                    }

                }
            }

            ans[i - 1] = count;
            count = 0;
        }
        Arrays.sort(ans);
        System.out.println(ans[n - 2]);
    }
}