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148 lars 1 
<?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_reverse;
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use function count;
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use function max;
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use SplFixedArray;
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final class TimeEfficientLongestCommonSubsequenceCalculator 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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        $common     = [];
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        $fromLength = count($from);
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        $toLength   = count($to);
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        $width      = $fromLength + 1;
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        $matrix     = new SplFixedArray($width * ($toLength + 1));
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        for ($i = 0; $i <= $fromLength; ++$i) {
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            $matrix[$i] = 0;
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        }
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        for ($j = 0; $j <= $toLength; ++$j) {
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            $matrix[$j * $width] = 0;
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        }
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        for ($i = 1; $i <= $fromLength; ++$i) {
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            for ($j = 1; $j <= $toLength; ++$j) {
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                $o = ($j * $width) + $i;
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                // don't use max() to avoid function call overhead
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                $firstOrLast = $from[$i - 1] === $to[$j - 1] ? $matrix[$o - $width - 1] + 1 : 0;
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                if ($matrix[$o - 1] > $matrix[$o - $width]) {
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                    if ($firstOrLast > $matrix[$o - 1]) {
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                        $matrix[$o] = $firstOrLast;
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                    } else {
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                        $matrix[$o] = $matrix[$o - 1];
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                    }
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                } else {
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                    if ($firstOrLast > $matrix[$o - $width]) {
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                        $matrix[$o] = $firstOrLast;
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                    } else {
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                        $matrix[$o] = $matrix[$o - $width];
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                    }
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                }
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            }
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        }
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        $i = $fromLength;
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        $j = $toLength;
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        while ($i > 0 && $j > 0) {
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            if ($from[$i - 1] === $to[$j - 1]) {
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                $common[] = $from[$i - 1];
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                --$i;
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                --$j;
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            } else {
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                $o = ($j * $width) + $i;
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                if ($matrix[$o - $width] > $matrix[$o - 1]) {
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                    --$j;
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                } else {
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                    --$i;
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                }
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            }
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        }
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        return array_reverse($common);
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    }
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}