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>

int main(void) {
  int n;
  int res=0;
  std::string s;
  std::cin >> n;
  std::cin >> s;
  int alphabet[26] = {};
  for(int xend=0;xend < n;xend++) {
    int tmp=0;
    for (int k=0;k < 26;k++) alphabet[k] = 0;
    for(int itr=0;itr <= xend;itr++) {
      for(int ybgn=xend+1;ybgn < n;ybgn++) {
        if(s[itr] == s[ybgn] && alphabet[s[itr]-'a']==0) alphabet[s[itr]-'a'] = 1;
      }
    }
    for (int k=0;k < 26;k++) tmp += alphabet[k];
    res = (tmp > res) ? tmp : res;
  }
  std::cout << res << std::endl;
  return 0;
}