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: Wrong Answer)

#include <iostream>
#include <string>
#include <vector>
#include <algorithm>

using namespace std;
int main(){
	int N;
	char S[1000];
	int count=0;
	cin >> N;
	std::vector<char> v;       
	int k=0;
	for(int i=1; i<=N; i++){
		cin >> S[i];
	}
	for(int j=1; j<=(N/2); j++){
		if(N%2 == 0){
			for(k=((N/2)+1); k<=N; k++){
				if(S[j]==S[k]) v.push_back(S[j]);
			}
		}else{
			for(k=((N+1)/2); k<=N; k++){
				if(S[j]==S[k]) v.push_back(S[j]);;
			}
		}
	}
	v.erase(std::unique(v.begin(), v.end()), v.end());	
	count = v.size();
	cout << count << endl;

	return 0;
}