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

int main(){
    int n; cin >> n;
    string s; cin >> s;
    int max_intersection=0;
    for (int i=1;i<n;i++){
        vector<char> v;
        vector<char> left(s.begin(), s.begin()+i);
        vector<char> right(s.begin()+i, s.end());
        sort(left.begin(), left.end());
        left.erase(unique(left.begin(), left.end()), left.end());
        sort(right.begin(), right.end());
        right.erase(unique(right.begin(), right.end()), right.end());

        auto point = set_intersection(left.begin(), left.end(), right.begin(), right.end(), back_inserter(v));
        sort(v.begin(), v.end());
        v.erase(unique(v.begin(), v.end()), v.end());
        if (v.size() >= max_intersection){
            max_intersection = v.size();
        }
    }
    cout << max_intersection << endl;
    return 0;
}