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;
typedef long long ll;

int main()
{
  int n, ans = 0;
  cin >> n;
  char s[100];
  scanf("%s", &s);

  for (int i = 1; i < n; i++)
  {
    map<char, int> l;
    map<char, int> r;
    int cnt = 0;
    for (int j = 0; j < i; j++)
    {
      l[s[j]]++;
    }
    for (int j = i; j < n; j++)
    {
      r[s[j]]++;
    }
    for (auto itrL = l.begin(); itrL != l.end(); itrL++)
    {
      for (auto itrR = r.begin(); itrR != r.end(); itrR++)
      {
        if (itrL->first == itrR->first)
        {
          cnt++;
          break;
        }
      }
    }
    ans = max(ans, cnt);
  }
  cout << ans << endl;
}