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 C (GCC 9.2.1) (judge verdict: Accepted)

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <stdbool.h>
#include <math.h>

int main(void){

    int N;

    scanf("%d", &N);

    char S[N+1];

    scanf("%s", S);

    int max = 0;

    for(int i = 0; i < N-1; i++){
        int x['z'-'a'+1], y['z'-'a'+1];
        for(int j = 0; j <= 'z'-'a'; j++){
            x[j] = 0;
            y[j] = 0;
        }
        for(int j = 0; j <= i; j++){
            x[S[j]-'a'] = 1;
        }
        for(int j = i+1; j < N; j++){
            y[S[j]-'a'] = 1;
        }
        int c = 0;
        for(int j = 0; j <= 'z'-'a'; j++){
            if(x[j] == 1 && y[j] == 1){
                c++;
            }
        }
        if(c > max){
            max = c;
        }
    }

    printf("%d\n", max);

    return 0;
}