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.HashSet;
import java.util.Scanner;
import java.util.Set;

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();
		sc.close();

		int ans = 0;
		for (int i = 1; i < n; i++) {
			Set<Character> set1 = new HashSet<>();
			for (int j = 0; j < i; j++) {
				set1.add(s.charAt(j));
			}
			Set<Character> set2 = new HashSet<>();
			for (int j = i; j < n; j++) {
				set2.add(s.charAt(j));
			}
			int cnt = 0;
			for (char c = 'a'; c <= 'z'; c++) {
				if (set1.contains(c) && set2.contains(c)) {
					cnt++;
				}
			}
			ans = Math.max(ans, cnt);
		}
		System.out.println(ans);
	}
}