Viewing file:  TimeEfficientLongestCommonSubsequenceImplementation.php (1.9 KB) -rw-r--r--
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<?php
/*
* This file is part of the Diff package.
*
* (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\LCS;
/**
* Time-efficient implementation of longest common subsequence calculation.
*/
class TimeEfficientImplementation implements LongestCommonSubsequence
{
/**
* Calculates the longest common subsequence of two arrays.
*
* @param array $from
* @param array $to
*
* @return array
*/
public function calculate(array $from, array $to)
{
$common = array();
$fromLength = count($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;
$matrix[$o] = max(
$matrix[$o - 1],
$matrix[$o - $width],
$from[$i - 1] === $to[$j - 1] ? $matrix[$o - $width - 1] + 1 : 0
);
}
}
$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);
}
}
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