TimeEfficientLongestCommonSubsequenceCalculator.php
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<?php declare(strict_types=1);
/*
* This file is part of sebastian/diff.
*
* (c) Sebastian Bergmann <sebastian@phpunit.de>
*
* For the full copyright and license information, please view the LICENSE
* file that was distributed with this source code.
*/
namespace SebastianBergmann\Diff;
use function array_reverse;
use function count;
use function max;
use SplFixedArray;
final class TimeEfficientLongestCommonSubsequenceCalculator implements LongestCommonSubsequenceCalculator
{
/**
* {@inheritdoc}
*/
public function calculate(array $from, array $to): array
{
$common = [];
$fromLength = count($from);
$toLength = count($to);
$width = $fromLength + 1;
$matrix = new SplFixedArray($width * ($toLength + 1));
for ($i = 0; $i <= $fromLength; ++$i) {
$matrix[$i] = 0;
}
for ($j = 0; $j <= $toLength; ++$j) {
$matrix[$j * $width] = 0;
}
for ($i = 1; $i <= $fromLength; ++$i) {
for ($j = 1; $j <= $toLength; ++$j) {
$o = ($j * $width) + $i;
// don't use max() to avoid function call overhead
$firstOrLast = $from[$i - 1] === $to[$j - 1] ? $matrix[$o - $width - 1] + 1 : 0;
if ($matrix[$o - 1] > $matrix[$o - $width]) {
if ($firstOrLast > $matrix[$o - 1]) {
$matrix[$o] = $firstOrLast;
} else {
$matrix[$o] = $matrix[$o - 1];
}
} else {
if ($firstOrLast > $matrix[$o - $width]) {
$matrix[$o] = $firstOrLast;
} else {
$matrix[$o] = $matrix[$o - $width];
}
}
}
}
$i = $fromLength;
$j = $toLength;
while ($i > 0 && $j > 0) {
if ($from[$i - 1] === $to[$j - 1]) {
$common[] = $from[$i - 1];
--$i;
--$j;
} else {
$o = ($j * $width) + $i;
if ($matrix[$o - $width] > $matrix[$o - 1]) {
--$j;
} else {
--$i;
}
}
}
return array_reverse($common);
}
}