Discussion on: Challenge: find 'Kaprekar numbers'

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This was a lot harder than I thought mainly because I had to look up why some numbers were and weren't Kaprekar numbers because the above description doesn't include all the details. First gotcha is the second part of the split numbers must be positive (no zeros). The second part was that you add a zero to the front if the length is odd.

<?php

$kaprekarNumbers = array();
$i = 1;

while (count ($kaprekarNumbers) < 8) {

  $square = $i * $i;
  if (strlen((string)$square) % 2  === 0) {
    $splitLength = strlen((string)$square) / 2;
  } else {
    $splitLength = round(strlen((string)$square) / 2);
    $square = "0".(string)$square;
  }

  $splitSquare = str_split((string)$square, $splitLength);

  if ((int)$splitSquare[1] != 0 && (int)$splitSquare[0]+(int)$splitSquare[1] == $i) {
    $kaprekarNumbers[] = $i;
  }

  $i++;
}


print_r($kaprekarNumbers);


?>

Richard Orelup • Nov 14 '17 • Edited

And I already refactored my answer. I'm happier with this one.

<?php

$kaprekarNumbers = array();
$i = 1;

while (count ($kaprekarNumbers) < 8) {

  $square = $i * $i;

  $splitLength = round(strlen((string)$square) / 2, 0, PHP_ROUND_HALF_DOWN);

  $splitFront = substr((string)$square, 0, $splitLength);
  $splitBack = substr((string)$square, $splitLength - strlen((string)$square));

  if ((int)$splitFront+(int)$splitBack == $i) {
    $kaprekarNumbers[] = $i;
  }

  $i++;
}

echo "\n\n".implode(",",$kaprekarNumbers)."\n\n";

?>

Peter Kim Frank • Nov 14 '17

Awesome job refactoring, and apologies for not including the pertinent info re: zeros in the OP!! I'll add that info to the main post.