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 9.2.1) (judge verdict: Accepted)

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

#define ll long long
#define ull unsigned long long 

int main(){
    int n;
    cin >> n;
    string s;
    cin >> s;

    int ans = 0;
    for(int i=0; i<n-1; ++i){
        string a= s.substr(0, i+1);
        string b= s.substr(i+1);

        set<char> s1(a.begin(), a.end());
        set<char> s2(b.begin(), b.end());

        // cout << a << "    " << b << endl;

        // for(auto x:s1)
        //     cout << x;
        //     cout << "      ";
        // for(auto x:s2)
        //     cout << x;
        // cout << endl << endl << endl;

        int count=0;
        for(int j=0; j<s1.size(); ++j){
            auto el = s1.begin();
            advance(el, j);
            if(binary_search(s2.begin(), s2.end(), *el))
                count++;
        }
        ans = max(ans, count);
    }
    cout << ans;
}