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>
#include <vector>
#include <algorithm>
#include <string>
#define rep(i, n) for(int i = 0; i < n; ++i)
using namespace std;

signed main() {
  ios::sync_with_stdio(false);
  cin.tie(0);

  int n;
  string s;
  cin >> n >> s;

  int ans = 0;
  for(int i = 1; i < n; ++i) {
    string x = s.substr(0, i);
    string y = s.substr(i, n-i);

    int cnt = 0;
    for(char c = 'a'; c <= 'z'; ++c) {
      bool isFoundx = false, isFoundy = false;
      rep(j, x.length()) {
        if(c==x[j]) isFoundx = true;
      }
      rep(j, y.length()) {
        if(c==y[j]) isFoundy = true;
      }
      if(isFoundx && isFoundy) ++cnt;
    }
    ans = max(ans, cnt);
  }
  cout << ans << '\n';
  return 0;
}