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<bits/stdc++.h>
using namespace std;

int main(){
    int N;
    cin >> N;
    string S;
    cin >> S;
    int max_count = 0;
    for (int i = 1; i < N; i++){
        string front;
        string back;
        front = S.substr(0, i);
        back = S.substr(i, N-i);
        set<char> front_set;
        set<char> back_set;
        for (int j = 0; j < i; j++){
            front_set.insert(front.at(j));
        }
        for (int j = 0; j < N - i; j++){
            back_set.insert(back.at(j));
        }
        int count = 0;
        for (char c : front_set){
            if (back_set.count(c)){
                count++;
            }
        }
        max_count = max(max_count, count);
    }
    cout << max_count << endl;
}