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) throws Exception {
		Scanner sc = new Scanner(System.in);
		int N = sc.nextInt();
		String S = sc.next();
		int ans = 0;
		for (int i = 0; i < S.length(); i++) {
			char[] first = S.substring(0, i + 1).toCharArray();
			char[] last = S.substring(i + 1, S.length()).toCharArray();
			int[] alpha_f = new int[26];
			int[] alpha_l = new int[26];
			for (int j = 0; j < first.length; j++) {
				alpha_f[first[j] - 'a']++;
			}
			for (int j = 0; j < last.length; j++) {
				alpha_l[last[j] - 'a']++;
			}
			int count = 0;
			for (int j = 0; j < 26; j++) {
				if (alpha_f[j] > 0 && alpha_l[j] > 0) {
					count++;
				}
			}
			ans = Math.max(ans, count);

		}
		System.out.println(ans);
		sc.close();
	}
}