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,max=0,i,j;
  scanf("%d",&n);
  char s[n+1];
  scanf("%s",s);
  int str[27][2];
  for(i=0;i<26;i++){
    str[i][0]=-1;
    str[i][1]=-1;
  }
  for(i=0;i<n;i++){
    if(str[s[i]-'a'][0]==-1)
      str[s[i]-'a'][0]=i+1;
    else
      str[s[i]-'a'][1]=i+1;
  }
  for(i=1;i<n;i++){
    int count=0;
    for(j=0;j<26;j++){
      if(str[j][0]<i && i<=str[j][1])
        count++;
    }
    if(max<count)
      max=count;
  }
  printf("%d\n",max);
  return 0;
}