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>

int main(){
		int n;
		scanf("%d",&n);
		char s[n];
		int hai[26][2]={0,0};
		int flag[26]={0};
		scanf("%s",s);
		int i;
		for(i=0;i<n;i++){
				if(flag[s[i]-'a']==0){
						hai[s[i]-'a'][0]=i;
						flag[s[i]-'a']=1;
				}
				hai[s[i]-'a'][1]=i;
		}
		int max=0,tmp=0,j;
		for(i=0;i<n-1;i++){
				tmp=0;
				for(j=0;j<26;j++){
						if(flag[j]!=0){
								if(i>=hai[j][0]&&i<hai[j][1])tmp++;
						}
				}
				if(tmp>max){
						max=tmp;
				}
		}
		printf("%d\n",max);
		return 0;
}