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 (GCC 5.4.1) (judge verdict: Accepted)

#include<stdio.h>
#include<string.h>
char s[1000];
int len;
int book1[27];
int book2[27];
void see1_book(int a,int b)
{
	int i;
	int shu;
	for(i=0;i<=b;i++)
	{
		shu=s[i]-96;
		book1[shu]=1;
	}
	return;
}
void see2_book(int a,int b)
{
	int i=0;
	int shu;
	for(i=a;i<=len-1;i++)
	{
		shu=s[i]-96;
		book2[shu]=1;
	}
	return;
}
int main()
{
	int N;
	scanf("%d",&N);
	getchar();
	gets(s);
	len=strlen(s);
	int i=0,count=0,j;
	int max=-1;
	for(i;i<=len-2;i++)
	{
		count=0;
		see1_book(0,i);
		see2_book(i+1,len-1);
		for(j=1;j<=26;j++)
		{
			if(book1[j]==1&&book2[j]==1)
			count++;
		}
		for(j=1;j<=26;j++)
		{
			book1[j]=0;
			book2[j]=0;
		}
		if(count>max)
		max=count;
	}
	printf("%d",max);
}