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 S = sc.next();
    
    int max = 0;
    for (int i = 1; i < N-1; i++) {
      int num = calc(S, i);
      if (num > max) {
        max = num;
      }
    }
    
    System.out.println(max);
  }
  
  private static int calc(String s, int pos) {

    int[] left = new int[26];
    for (int i = 0; i <= pos-1; i++) {
      left[s.charAt(i) - 'a'] = 1;
    }

    int ret = 0;
    for (int i = pos; i < s.length(); i++) {
      if (left[s.charAt(i) - 'a'] == 1) {
        left[s.charAt(i) - 'a'] = 0;
        ret++;
      }
    }

    return ret;
  }
}