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 check(string x, string y){
  map<char, bool> m;
  map<char, bool> m2;
  
  int ret = 0;
  for(int i = 0; i < x.size(); i++){
    m[x[i]] = true;
  }
  for(int i = 0; i < y.size(); i++){
    m2[y[i]] = true;
  }

  for(auto x: m2){
    if(m.count(x.first) != 0){
      ret++;
    }
  }
  return ret;
}

int main(){
  int N;
  string S;
  cin >> N;
  cin >> S;
  cerr << check("hoge", "huge") << endl;
  
  int tmpans = 0;
  for(int i = 0; i < N; i++){
    string x,y;
    x = S.substr(0, i);
    y = S.substr(i, N-i);
    // cerr << x << " " << y << endl;
    int tmp = check(x,y);
    if(tmp > tmpans){
      tmpans = tmp;
    }
  }
  cout << tmpans << endl;
}