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 PHP7 (7.0.15) (judge verdict: Accepted)

<?php
  //分ける場所を移動させてく.
  //左側を切り分ける
  //右側をfor文で回して in_array
fscanf(STDIN,"%d",$n);
fscanf(STDIN,"%s",$s);

//$a_li=explode(" ",trim(fgets(STDIN)));

$c=0;
$max=0;

for($i=1;$i<$n;$i++){
  $tmp_s=$s;
  $right_s = substr($s, $i);  // abcd
  $left_s = str_replace($right_s,'',$tmp_s);
  $right_s = array_unique(str_split($right_s));
  $left_s= str_split($left_s);
  foreach($right_s as $v){
    if(in_array($v,$left_s)){
      $c++;
    }
  }
  $max=max($c,$max);
  $c=0;
}

echo $max."\n";