function TimeEfficientLongestCommonSubsequenceCalculator::calculate

@inheritDoc

Overrides LongestCommonSubsequenceCalculator::calculate

File

vendor/sebastian/diff/src/TimeEfficientLongestCommonSubsequenceCalculator.php, line 22

Class

TimeEfficientLongestCommonSubsequenceCalculator

Namespace

SebastianBergmann\Diff

Code

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);
}