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 <cstdio>
#include <cstring>
#include <queue>
#include <algorithm>

using namespace std;

char s[200];
int ll[100] , rr[100] , n;

int solve(int x)
{
	int ttt = 0;
	memset(ll , 0 , sizeof(ll));
	memset(rr , 0 , sizeof(rr));
	for(int i = 0 ; i <= x ; i++){
		ll[s[i] - 'a']++;
	}
	for(int i = x + 1 ; i < n ; i++){
		rr[s[i] - 'a']++;
	}
	for(int i = 0 ; i < 26 ; i++){
		if(rr[i] != 0 && ll[i] != 0) ttt++;
	}
	return ttt;
}

int main()
{
	scanf("%d",&n);
	scanf("%s",s);
	int Max = -1;
	for(int i = 0 ; i < n ; i++){
		Max = max(Max , solve(i));
	}
	printf("%d\n",Max);
}