Worst Practice

Today’s puzzle in short: we get a bunch of random characters and need to find the first n distinct characters.

The input data

Today there’s only one line in the input, but it’s a long one. No special rules for this, just a bunch of characters.

Our task is to find the position of the first n distinct characters.

Part one and two

The two parts today are almost the same, the only difference is the value of the n:

• In part one, n is 4.
• In part two, n is 14.

In the solution today I can simply read the whole input at once, since it contains only one line. Then we split this long string into array with the str_split() function, that I used before. Then just start counting. Make it simple:

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19

              
              

                
$line = file_get_contents(__DIR__.'/input.txt');
$code = str_split($line);
$buffer = [];
const MARKER_LENGTH = 4;

for ($i = 0; $i < count($code); $i++) {
    if (in_array($code[$i], $buffer)) {
        [, $buffer] = explode($code[$i], implode('',$buffer));
        $buffer = empty($buffer) ? [] : str_split($buffer);
    }

    $buffer[] = $code[$i];

    if (count($buffer) == MARKER_LENGTH) {
        break;
    }
}

echo ($i + 1).PHP_EOL;

              
            
          
        
      

The only complexity in this story the buffer handling. I chose a very primitive and low performance, but yet effective way:

• check if the next character is in the buffer
  • if yes, then convert the buffer to string
  • split by the next character and take the second part
  • convert this to array again, or initialize an empty array if the second part is empty
• add the new character to the buffer
• quit the loop when the buffer reached the MARKER_LENGTH