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: Wrong Answer)

#include <stdio.h>
#include <string.h>
int main(void){
    int n;
    char s[100+5];
    scanf("%d", &n);
    scanf("%s", s);
    
    int ans=0;
    for(int i=1; i<n; i++){
        char x[100+5], y[100+5];
        strncpy(x, s, i);
        x[i]='\0';
        strncpy(y, s+i, n-i);
        y[n-i]='\0';
        
        int c=0;    // count;
        int alpha[30];  // x, yで使われたalphabet
        for(int j=0; j<strlen(x); j++)alpha[x[j]-'a']=1;
        for(int j=0; j<strlen(y); j++){
            if(alpha[y[j]-'a']==1){
                c++;
                alpha[y[j]-'a']=0;
            }
        }
        if(c>ans)ans=c;
        // printf("%s %s %d\n", x, y, c);
    }
    
    printf("%d\n", ans);
    
    return 0;
}