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.*;

class Main{
	public static void main(String[] A){
		Scanner s=new Scanner(System.in);
		int n=s.nextInt();
		char[]c=s.next().toCharArray();
		int[]l=new int[26],r=new int[26];
		int v=0;
		for(char i:c)
			++r[i-'a'];
		for(char i:c) {
			--r[i-'a'];
			++l[i-'a'];
			int k=0;
			for(int j=0;j<26;++j)
				if(r[j]>0&&l[j]>0)
					++k;
			v=Math.max(v,k);
		}
		System.out.println(v);
	}
}