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 = sc.nextInt();
    String str = sc.next();
    int max_count = 0;
    int count;
    char alphabet;

    for (int i = 0; i <= N; i++) {
      count = 0;
      alphabet = 'a';

      String str1 = str.substring(0, i);
      String str2 = str.substring(i, N);

      for (int j = 0; j <= 25; j++) {
        char tmp_alpha = alphabet++;
        if (str1.contains(String.valueOf(tmp_alpha)) && str2.contains(String.valueOf(tmp_alpha))) {
          count += 1;
        }
      }

      max_count = Math.max(max_count, count);
    }

    System.out.println(max_count);
  }
}