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<?php |
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namespace Coyote\Services\Parser\Parsers\Parentheses; |
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use Tests\Feature\Services\Parser\Parsers\Parentheses\ParenthesesParserTest; |
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/** |
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* If you read {@link ParenthesesParserTest} you will see examples, of how this |
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* class works. |
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* |
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* This class responsibility is to use symmetric or mismatched chunks returned |
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* by {@link SymmetricParenthesesChunks} and "comb" them into valid/invalid |
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* parentheses expressions. It is done in two steps: |
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* - Combing: |
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* - Iterates chunks first by pairs (if nestLevel is >= 0). |
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* - Then, iterates by triplets (if nestLevel is >= 1). |
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* - Then, iterates chunks by four of each (if nestLevel is >= 2), and so on |
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* Algorithm complexity is: o(n * c), where: |
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* - `n` - is the number of chunks, which is number of symmetric parentheses in input string divided by two. |
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* - `l` - nestLevel |
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* So for nestLevel=chunks (n=l), complexity is: o(n^2) |
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* After combing, `l` levels of parentheses should be joined into one. (So for example, |
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* for nestLevel=6, parentheses nested 7 times won't be parsed). |
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* - Squashing |
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* - Joins any two valid adjacent chunks into one, so they can be later for example |
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* rendered as a single link. |
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*/ |
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class ParenthesesParser |
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{ |
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/** @var SymmetricParenthesesChunks */ |
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private $chunks; |
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/** @var int */ |
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private $nestLevel; |
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public function __construct(SymmetricParenthesesChunks $chunks, int $nestLevel) |
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{ |
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$this->chunks = $chunks; |
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$this->nestLevel = $nestLevel; |
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} |
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public function parse(string $content): array |
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{ |
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$chunks = $this->chunks->chunk($content); |
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$chunks = $this->comb($chunks, 1); |
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$chunks = $this->flatMapMismatched($chunks); |
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$chunks = $this->comb($chunks, $this->nestLevel - 1); |
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$chunks = $this->squashChunks($chunks); |
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return $chunks; |
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} |
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private function comb(array $elements, int $iterations): array |
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{ |
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$result = $elements; |
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for ($i = 0; $i < $iterations; $i++) { |
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$result = $this->performCombIteration($result, $i + 1); |
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} |
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return $result; |
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} |
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private function performCombIteration(array $elements, int $nestLevel): array |
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{ |
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// for $nestLevel < 0 this method doesn't make any sense |
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// for $nestLevel = 0 this method doesn't have any effect |
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if ($nestLevel < 0) { |
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throw new \InvalidArgumentException(); |
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} |
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$result = []; |
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for ($i = 0; $i < count($elements); $i++) { |
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$toComb = join(array_slice($elements, $i, $nestLevel + 1)); |
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if ($this->validExpression($toComb)) { |
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$result[] = $toComb; |
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$i += $nestLevel; |
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continue; |
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} |
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$result[] = $elements[$i]; |
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} |
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return $result; |
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} |
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private function flatMapMismatched(array $elements): array |
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{ |
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$result = []; |
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foreach ($elements as $element) { |
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if ($this->validExpression($element)) { |
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$result[] = $element; |
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} else { |
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$result = array_merge($result, pattern('([()])')->split($element)); |
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} |
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} |
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return array_values(array_filter($result, 'strlen')); |
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} |
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private function squashChunks(array $chunks): array |
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{ |
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$result = []; |
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$squashedChunks = null; |
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foreach ($chunks as $chunk) { |
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if ($this->validExpression($chunk)) { |
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$squashedChunks .= $chunk; |
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} else { |
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if ($squashedChunks !== null) { |
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$result[] = $squashedChunks; |
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$squashedChunks = null; |
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} |
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$result[] = $chunk; |
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} |
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} |
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if ($squashedChunks !== null) { |
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$result[] = $squashedChunks; |
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} |
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return $result; |
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} |
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private function validExpression(string $expression): bool |
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{ |
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return mb_substr_count($expression, '(') === mb_substr_count($expression, ')'); |
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// Technically, ")(" would also be considered a valid expression, |
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// but `ParenthesesChunks` will not return such chunks. |
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} |
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} |
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adam-boduch /
coyote
If the size of the collection does not change during the iteration, it is generally a good practice to compute it beforehand, and not on each iteration: