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: Wrong Answer)

#include <stdio.h>

int main() {
  int NUM;
  int MAX=0;
  char c[101];
  
  int cnt_same=0;
  
  int reg_same_left[26];
  int reg_same_right[26];
  
  scanf("%d", &NUM);
  scanf("%s", c);
      
  // Init
  for (int j=0; j<26; j++) {
    reg_same_left[j] = 0;
    reg_same_right[j] = 0;  
  }
  
  for (int i=0; i<(NUM-1); i++) {
    cnt_same = 0;
    
    // Check Char Left Side
    for (int j=0; j<i; j++) {
      reg_same_left[c[j] - 0x61] |= 1; 
    }
    // Check Char Right Side
    for (int j=i; j<NUM; j++) {
      reg_same_right[c[j] - 0x61] |= 1; 
    }
    // Count
    for (int j=0; j<26; j++)
      cnt_same += (reg_same_left[j] * reg_same_right[j]);
    
    if (cnt_same > MAX)
      MAX = cnt_same;
  }
  printf("%d", MAX);
  return 0;
}