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.Scanner;

public class Main {
	public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);
		int n = scan.nextInt();
		String s = scan.next();
		char[] c = new char[n];
		int[] count = new int[n];
		int a = 'a';
		int max = 0;
		for (int i = 0; i < n; i++) {
				c[i] = s.charAt(i);
		}
		for (int i = 1; i < n; i++) {
			boolean[] xmemo = new boolean[26];
			boolean[] ymemo = new boolean[26];
			for (int j = 0; j < i; j++) {
				xmemo[c[j]-a] = true;
			}
			for (int k = i; k < n; k++) {
				ymemo[c[k]-a] = true; 
			}
			for (int l = 0; l < 26; l++) {
				if (xmemo[l] && ymemo[l])	 count[i]++;
			}
		}
		for (int i = 0; i < n; i++) {
			if (count[i] > max) {
				max = count[i];
			}
		}
		System.out.println(max);
	}
}