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.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

class Main{
	public static void main(String[] args) throws NumberFormatException, IOException {
		BufferedReader bfr=new BufferedReader(new InputStreamReader(System.in));
		int[] alp1=new int[26];
		int[] alp2=new int[26];
		int mjs=Integer.parseInt(bfr.readLine());
		String uketuke=bfr.readLine();
		char[] ret=new char[mjs];
		int max=0;
		int counter=0;
		for(int i=0; i<mjs; i++) {
			ret[i]=uketuke.charAt(i);
		}

		for(int i=0; i<mjs; i++) {
			counter=0;
			for(int j=0; j<i; j++) {
				alp1[ret[j]*1-97]++;
			}
			for(int j=i; j<mjs; j++) {
				alp2[ret[j]*1-97]++;
			}

			for(int j=0; j<26; j++) {
				if(alp1[j]>0 &&alp2[j]>0) {
					counter++;
				}
				alp1[j]=0;
				alp2[j]=0;
			}
			if(counter>max) {
				max=counter;
			}
		}
		System.out.println(max);
	}
}