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

int main() {
  int N, cnt=0, max=0;
  vector<int> A(26), B(26);
  string S;
  cin >> N >> S;
  for(int i=1; i<N-1; i++){
    for(int j=0; j<i; j++){
      A.at(S.at(j)-'a')++;
    }
    for(int k=i; k<S.size(); k++){
      B.at(S.at(k)-'a')++;
    }
    for(int l=0; l<26; l++){
      if(A.at(l)>0 && B.at(l)>0){
        cnt++;
      }
    }
    if(max<cnt) max=cnt;
    cnt=0;
    for(int m=0; m<26; m++){
      A.at(m)=0;
      B.at(m)=0;
    }
  }
  cout << max << endl;
}