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++14 (GCC 5.4.1) (judge verdict: Accepted)

#include <iostream>
#include <algorithm>
#include <string>
using namespace std;

int main() {
	int n;
	string k;
	cin >> n >> k;
	int s[100];
	for (int i = 0; i < n; i++)
		s[i] = k[i] - 97;
	int max = 0;
	int countf = 0, countb = 0, count = 0;
	for (int i = 1; i < n; i++) {
		for (int j = 0; j < 26; j++) {
			for (int k = 0; k < i; k++)
				if (s[k] == j)
					countf++;
			for (int k = i; k < n; k++)
				if (s[k] == j)
					countb++;
			if (countf > 0 && countb > 0)
				count++;
			countf = 0;
			countb = 0;
		}
		if (max < count)
			max = count;
		count = 0;
	}
	cout << max << endl;
	return 0;
}