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;
#define rep(i,n) for (int i = 0; i < (n); ++i)

int main() {
    int N,r=0;
    string S;
    cin >> N >> S;
    map<char,int> l;
    set<char> f;

    rep(i,N) {
        if(!l.count(S.at(i)))
            l[S.at(i)] = 1;
        else
            l.at(S.at(i))++;
    }

    rep(i,N) {
        int c=0;
        l.at(S.at(i))--;
        if(l.at(S.at(i)) == 0)
            l.erase(S.at(i));

        f.insert(S.at(i));
        for(char t : f)
            if(l.count(t))
                c++;
        r = max(r,c);
    }

    cout << r << endl;
}