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.nextLine());
    String S = sc.next();
    boolean[] b = new boolean[26];
    
    int ans = 0;
    for(int i = 1; i <= N; i++){
      String s1 = new String(S.substring(0, i));
      String s2 = new String(S.substring(i, N));
      for(int j = 0; j < s1.length(); j++){
        char c = s1.charAt(j);
        b[c-'a'] = true;
      }
      
      int count = 0;
      for(int j = 0; j < s2.length(); j++){
        char c = s2.charAt(j);
        if(b[c-'a']){
          count++;
          b[c-'a'] = false;
        }
      }
      ans = ans < count ? count : ans;
    }    
    System.out.println(ans);
  }
}