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.*;
 
public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int N = Integer.parseInt(sc.next());
        String S = sc.next();
        String x = "";
        String y = "";
        int max = 0;
        for(int i=1; i <= N-1; i++) {
            x = S.substring(0, i);
            y = S.substring(i, N);
            List<String> l = new ArrayList<>();
            String[] xs = x.split("");
            String[] ys = y.split("");
            int count = 0;
            for(String s : xs) {
                if(l.contains(s)) continue;
                else l.add(s);
            }
            for(String s : ys) {
                if(l.contains(s)) count++; l.remove(s);
            }
            if(max < count) {
                max = count;
            }
        }
        System.out.println(max);
    }
}