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MemoryEfficientLongestCommonSubsequenceCalculator.php
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MemoryEfficientLongestCommonSubsequenceCalculator.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_fill;
use function array_merge;
use function array_reverse;
use function array_slice;
use function count;
use function in_array;
use function max;
final class MemoryEfficientLongestCommonSubsequenceCalculator implements LongestCommonSubsequenceCalculator
{
/**
* {@inheritdoc}
*/
public function calculate(array $from, array $to): array
{
$cFrom = count($from);
$cTo = count($to);
if ($cFrom === 0) {
return [];
}
if ($cFrom === 1) {
if (in_array($from[0], $to, true)) {
return [$from[0]];
}
return [];
}
$i = (int) ($cFrom / 2);
$fromStart = array_slice($from, 0, $i);
$fromEnd = array_slice($from, $i);
$llB = $this->length($fromStart, $to);
$llE = $this->length(array_reverse($fromEnd), array_reverse($to));
$jMax = 0;
$max = 0;
for ($j = 0; $j <= $cTo; $j++) {
$m = $llB[$j] + $llE[$cTo - $j];
if ($m >= $max) {
$max = $m;
$jMax = $j;
}
}
$toStart = array_slice($to, 0, $jMax);
$toEnd = array_slice($to, $jMax);
return array_merge(
$this->calculate($fromStart, $toStart),
$this->calculate($fromEnd, $toEnd)
);
}
private function length(array $from, array $to): array
{
$current = array_fill(0, count($to) + 1, 0);
$cFrom = count($from);
$cTo = count($to);
for ($i = 0; $i < $cFrom; $i++) {
$prev = $current;
for ($j = 0; $j < $cTo; $j++) {
if ($from[$i] === $to[$j]) {
$current[$j + 1] = $prev[$j] + 1;
} else {
// don't use max() to avoid function call overhead
if ($current[$j] > $prev[$j + 1]) {
$current[$j + 1] = $current[$j];
} else {
$current[$j + 1] = $prev[$j + 1];
}
}
}
}
return $current;
}
}

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