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 in = new Scanner(System.in);
        in.nextLine();
        String s = in.nextLine();
        int[] l = new int[26], r = new int[26];
        for(char ch : s.toCharArray()) {
            r[ch - 'a']++;
        }
        int ans = 0;
        for(char ch : s.toCharArray()) {
            r[ch - 'a']--; l[ch - 'a']++;
            ans = Math.max(ans, findSameChars(l, r));
        }
        System.out.println(ans);
    }

    public static int findSameChars(int[] a, int[] b) {
        int ans = 0;
        for(int i = 0; i < 26; i++) {
            if(a[i] > 0 && b[i] > 0) ans++;
        }
        return ans;
    }
}