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 <iostream>
#include <string>

using namespace std;

int main(void) {

  int num = 0;
  int N;
  string S;
  string alphabet = "abcdefghijklmnopqrstuvwxyz";

  cin >> N;
  cin >> S;

  for (int i = 0; i < N; ++i) {
    int tmp = 0;
    string S1 = S.substr(0, i);
    string S2 = S.substr(i, N - i);

    // cout << S1 << endl;
    // cout << S2 << endl;

    for (auto it = alphabet.cbegin(); it != alphabet.cend(); ++it) {
      if (S1.find(*it) != string::npos && S2.find(*it) != string::npos) tmp += 1;
    }
    
    num = max(tmp, num);
  }

  cout << num << endl;
  
  return 0;
}