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: Wrong Answer)

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

int main(){
  int N;
  string s;
  cin >>N>>s;
  vector<int> abc(26,0);
  int ans;
  int ma = 0;
  for(int i=1;i<N;i++){
    ans = 0;
    for(int j=0;j<i;j++){
      int x;
      x = s[j];
      x -=97;
      abc.at(x) = 1;
    }
    for(int j=i;j<N;j++){
      int y;
      y = s[j];
      y -= 97;
      if(abc.at(y) == 1) ans++;
    }
    ma = max(ma,ans);
  }
  cout << ma << endl;
}