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.Scanner;

public class Main {

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int N = sc.nextInt();
        String S = sc.next();
        sc.close();
        int[] alp = new int[26];
        int[] cnt = new int[N];
        for(int i = 0; i < N; i++){
            char s = S.charAt(i);
            alp[s - 97]++;
            cnt[i] = alp[s - 97];
        }
        int[] dp = new int[N+1];
        int ans = 0;
        for(int i = 0; i < N; i++){
            char s = S.charAt(i);
            if(cnt[i] == 1 && alp[s - 97] > 1) dp[i+1] = dp[i] + 1;
            else if(cnt[i] == 1 && alp[s - 97]== 1) dp[i+1] = dp[i];
            else if(cnt[i] > 1 && cnt[i] < alp[s - 97]) dp[i+1] = dp[i];
            else dp[i+1] = dp[i] -1;
            ans = Math.max(ans, dp[i+1]);
        }
        System.out.println(ans);

    }

}