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 <string>
#include <vector>
#include <map>
#include <algorithm>
using namespace std;

int main()
{
    int n;
    string s;
    cin >> n >> s;
    std::map<char, int> x{};
    std::map<char, int> y{};
    std::map<char, bool> dual{};
    for (int i = 0; i < n; i++) {
        y[s[i]]++;
        dual[s[i]] = false;
    }
    std::vector<int> vec{};
    for (int i = 0; i < n; i++) {
        x[s[i]]++;
        y[s[i]]--;
        if (y[s[i]] > 0) {
            dual[s[i]] = true;
        } else {
            dual[s[i]] = false;
        }
        int num = 0;
        for (auto& x : dual)
            num += x.second;
        vec.push_back(num);
    }
    std::cout << *std::max_element(vec.begin(), vec.end()) << std::endl;

    return 0;
}