89 lines
2.2 KiB
PHP
89 lines
2.2 KiB
PHP
<?php declare(strict_types=1);
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/*
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* This file is part of sebastian/diff.
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*
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* (c) Sebastian Bergmann <sebastian@phpunit.de>
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*
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* For the full copyright and license information, please view the LICENSE
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* file that was distributed with this source code.
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*/
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namespace SebastianBergmann\Diff;
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use function array_fill;
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use function array_merge;
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use function array_reverse;
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use function array_slice;
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use function count;
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use function in_array;
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use function max;
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final class MemoryEfficientLongestCommonSubsequenceCalculator implements LongestCommonSubsequenceCalculator
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{
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/**
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* {@inheritdoc}
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*/
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public function calculate(array $from, array $to): array
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{
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$cFrom = count($from);
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$cTo = count($to);
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if ($cFrom === 0) {
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return [];
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}
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if ($cFrom === 1) {
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if (in_array($from[0], $to, true)) {
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return [$from[0]];
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}
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return [];
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}
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$i = (int) ($cFrom / 2);
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$fromStart = array_slice($from, 0, $i);
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$fromEnd = array_slice($from, $i);
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$llB = $this->length($fromStart, $to);
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$llE = $this->length(array_reverse($fromEnd), array_reverse($to));
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$jMax = 0;
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$max = 0;
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for ($j = 0; $j <= $cTo; $j++) {
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$m = $llB[$j] + $llE[$cTo - $j];
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if ($m >= $max) {
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$max = $m;
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$jMax = $j;
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}
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}
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$toStart = array_slice($to, 0, $jMax);
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$toEnd = array_slice($to, $jMax);
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return array_merge(
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$this->calculate($fromStart, $toStart),
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$this->calculate($fromEnd, $toEnd)
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);
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}
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private function length(array $from, array $to): array
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{
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$current = array_fill(0, count($to) + 1, 0);
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$cFrom = count($from);
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$cTo = count($to);
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for ($i = 0; $i < $cFrom; $i++) {
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$prev = $current;
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for ($j = 0; $j < $cTo; $j++) {
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if ($from[$i] === $to[$j]) {
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$current[$j + 1] = $prev[$j] + 1;
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} else {
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$current[$j + 1] = max($current[$j], $prev[$j + 1]);
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}
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}
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}
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return $current;
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}
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}
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