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<?php |
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declare(strict_types=1); |
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namespace CoenMooij\Sudoku\Solver; |
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use CoenMooij\Sudoku\Exception\UnsolvableException; |
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use CoenMooij\Sudoku\Puzzle\Grid; |
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use CoenMooij\Sudoku\Puzzle\Location; |
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/** |
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* Informed depth first search. |
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*/ |
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class BacktrackSolver implements GridSolverInterface |
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{ |
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private const DIRECTION_FORWARDS = true; |
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private const DIRECTION_BACKWARDS = false; |
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/** |
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* @var Grid |
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*/ |
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private $grid; |
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/** |
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* @var int[][][] |
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*/ |
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private $possibleValues; |
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/** |
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* @var bool[][] |
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*/ |
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private $presetValues; |
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/** |
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* @var bool |
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*/ |
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private $direction; |
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/** |
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* @var int |
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*/ |
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private $row; |
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/** |
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* @var int |
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*/ |
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private $column; |
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public function solve(Grid $grid): Grid |
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{ |
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$this->initialize($grid); |
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while ($this->locationIsValid()) { |
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if (!$this->isPresetValue()) { |
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$this->direction === self::DIRECTION_FORWARDS |
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? $this->handleForwardsIteration() |
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: $this->handleBackwardsIteration(); |
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} |
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$this->nextLocation(); |
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} |
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if (!$this->reachedEndOfGrid()) { |
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throw new UnsolvableException(); |
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} |
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return $grid; |
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} |
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private function handleForwardsIteration(): void |
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{ |
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$this->findAllPossibleValuesForCurrentLocation(); |
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if ($this->currentLocationHasPossibleValues()) { |
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$this->fillCurrentLocationWithNextPossibleValue(); |
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} else { |
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$this->grid->empty($this->getCurrentLocation()); |
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$this->direction = self::DIRECTION_BACKWARDS; |
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} |
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} |
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private function handleBackwardsIteration(): void |
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{ |
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if ($this->currentLocationHasPossibleValues()) { |
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$this->fillCurrentLocationWithNextPossibleValue(); |
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$this->direction = self::DIRECTION_FORWARDS; |
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} else { |
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$this->grid->empty($this->getCurrentLocation()); |
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} |
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} |
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private function initialize(Grid $grid): void |
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{ |
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$this->direction = self::DIRECTION_FORWARDS; |
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$this->column = 0; |
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$this->row = 0; |
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$this->grid = $grid; |
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$this->possibleValues = []; |
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$this->presetValues = []; |
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$this->initializePresetValues(); |
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} |
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private function initializePresetValues(): void |
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{ |
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for ($row = 0; $row < 9; $row++) { |
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for ($column = 0; $column < 9; $column++) { |
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$location = new Location($row, $column); |
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if ($this->grid->isEmpty($location)) { |
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$this->presetValues[$row][$column] = false; |
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} else { |
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$this->presetValues[$row][$column] = true; |
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} |
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} |
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} |
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} |
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private function currentLocationHasPossibleValues(): bool |
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{ |
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return !empty($this->possibleValues[$this->row][$this->column]); |
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} |
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private function findAllPossibleValuesForCurrentLocation(): void |
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{ |
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$possibilities = $this->grid->getAllPossibilitiesFor(new Location($this->row, $this->column)); |
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shuffle($possibilities); |
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$this->possibleValues[$this->row][$this->column] = $possibilities; |
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} |
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private function nextLocation(): void |
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{ |
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if ($this->direction === self::DIRECTION_FORWARDS) { |
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$this->row = $this->column === 8 ? $this->row + 1 : $this->row; |
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$this->column = $this->column === 8 ? 0 : $this->column + 1; |
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} else { |
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$this->row = $this->column === 0 ? $this->row - 1 : $this->row; |
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$this->column = $this->column === 0 ? 8 : $this->column - 1; |
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} |
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} |
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private function fillCurrentLocationWithNextPossibleValue(): void |
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{ |
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$this->grid->set($this->getCurrentLocation(), $this->possibleValues[$this->row][$this->column][0]); |
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array_shift($this->possibleValues[$this->row][$this->column]); |
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} |
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private function getCurrentLocation(): Location |
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{ |
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return new Location($this->row, $this->column); |
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} |
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private function isPresetValue(): bool |
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{ |
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return !empty($this->presetValues[$this->row][$this->column]); |
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} |
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private function locationIsValid(): bool |
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{ |
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return $this->row >= 0 && $this->row < 9; |
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} |
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private function reachedEndOfGrid(): bool |
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{ |
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return $this->row > 8; |
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} |
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} |
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coenmooij /
sudoku
