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.ArrayList;
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 ans = 0;
		for(int n=2; n<N; n++) {
			int tmp=0;
			ArrayList Xlist = new ArrayList();
			for(int i=0;i<n;i++) {
				if(!Xlist.contains(S.charAt(i)))
					Xlist.add(S.charAt(i));
			}
			String Y = S.substring(n, N);
			for(int i=n;i<N;i++) {
				if(Xlist.contains(S.charAt(i))) {
					tmp++;
					Xlist.remove(Xlist.indexOf(S.charAt(i)));
				}
			}
			if(ans<tmp)
				ans = tmp;
		}
		System.out.println(ans);
	}
}