Sapo F25 Challenge

sapo_f25.php

<?php
/**
 * quick f15 prototype that should do what's needed
 * no item indexes to make it harder
 * `$items[$i] = 'item '. $i` would be too easy and even smaller
 */
function f15($page)
{
  $first = ($page - 1) * 15 + 1;
  for ($i = $first; $i < $first + 15; $i++)
  {
    $items[] = 'item ' . $i;
  }
  return $items;
}


/**
 * try at the f25 challenge
 */
function f25_big($page)
{
  // calculate the first page needed from f15
  $f15_page = $page + floor(2 * ($page - 1) / 3);

  // fetch 3 pages of items from f15 (sometimes we only need 2, but small code is the target)
  $f15_items = array_merge(f15($f15_page), f15($f15_page + 1), f15($f15_page + 2));

  // calculate the offset from the first page of items we got
  $f15_page_offset = 25 * ($page - 1) - 15 * ($f15_page - 1);

  // return the 25 items after this offset
  return array_splice($f15_items, $f15_page_offset, 25);
}


/**
 * f25 after shortening variables and math simplifications: 119 chars
 */
function f25($p){$f=floor((5*$p-2)/3);return array_splice(array_merge(f15($f),f15($f+1),f15($f+2)),25*$p-15*$f-10,25);}


// poor man's unit test
for ($i = 1; $i <= 10000; $i++)
{
  $items = f25($i);
  if ($items[0] != 'item ' . (($i - 1) * 25 + 1) || $items[24] != 'item ' . ($i * 25))
  {
    echo "Page ". $i . " » " . $items[0] . " to " . $items[24] . " » failed\n";
  }
}