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 <stdio.h>
#include <string>
#include <cstdlib>
#include <cmath>
#include <cstring>
#include <math.h>
#include <vector>
#include <algorithm>

using namespace std;

int diff_char(string s, int n){
	int cnt_l[26], cnt_r[26];
	for(int i=0; i<26; i++){
		cnt_l[i]=0;
		cnt_r[i]=0;
	}
	for(int i=0; i<n; i++){
		cnt_l[s[i]-'a']++;
	}
	for(int i=n; i<s.length(); i++){
		cnt_r[s[i]-'a']++;
	}
	int cnt=0;
	for(int i=0; i<26; i++){
		if(cnt_l[i]>0 && cnt_r[i]>0) cnt++;
	}
	return cnt;
}

int main(){
	int n;
	string s;
	cin >> n >> s;
	int max=0;
	for(int i=0; i<n; i++){
		int diff=diff_char(s,i);
		if(diff>max){
			max=diff;
		}
	}
	cout << max << endl;
	return 0;
}