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,ans=0;
  string s,f,l;
  char a;
  cin>>n>>s;
  for(int i=1;i<n-1;i++){
    int cnt=0;
    f=s.substr(0,i);
    l=s.substr(i,n-i);
    for(char c='a';c<='z';c++){
       bool fok=false,lok=false;
      for(int j=0;j<f.size();j++){
	if(f.at(j)==c)fok=true;
      }
      for(int j=0;j<l.size();j++){
	if(l.at(j)==c)lok=true;
      }
      if(fok&&lok)cnt++;
    }
    ans=max(ans,cnt);
  }
  cout<<ans<<endl;
  return 0;
}