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 5.4.1) (judge verdict: Accepted)

#include <stdio.h>
void initArray(int a[], int len);
int main(void)
{
    int n;
    scanf("%d\n", &n);
    char s[n];
    int alf[26];
    for (int i = 0; i < n; i++)
    {
        scanf("%c", &s[i]);
    }

    int mid = 1, max = 0;
    while (mid < n)
    {
        initArray(alf, 26);
        int num = 0;
        for (int i = 0; i < mid; i++)
        {
            int tmp = s[i] - 'a';
            alf[tmp] = 1;
        }
        for (int j = mid; j < n; j++)
        {
            int tmp = s[j] - 'a';
            if (alf[tmp] == 1)
            {
                alf[tmp]++;
            }
        }
        for (int k = 0; k < n; k++)
        {
            if (alf[k] == 2)
            {
                num++;
            }
        }
        if (num > max)
        {
            max = num;
        }
        mid++;
        // for(int i = 0; i< 26;i++)
        // {
        //     printf("%d ",alf[i]);
        // }
        // puts("");
    }

    printf("%d\n", max);
    return 0;
}

void initArray(int a[], int len)
{
    for (int i = 0; i < len; i++)
    {
        a[i] = 0;
    }
}