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 PHP (5.6.30) (judge verdict: Accepted)

<?php

fscanf(STDIN, '%d', $n);
fscanf(STDIN, '%s', $s);

$max = 0;
for ($i = 1; $i < $n; $i++) {
    $left = substr($s, 0, $i);
    $right = substr($s, $i);

    $array = str_split($left);
    $unique = array_unique($array);
    $array = array_values($unique);

    $cnt = 0;
    foreach ($array as $value) {
        if (strpos($right, $value) !== false) {
            $cnt++;
        }
    }
    if ($max < $cnt) {
        $max = $cnt;
    }
}

echo $max;