PHP-Code

<?php

class Sudoku
{
	private $field = [];
	
	public function __construct ()
	{
		$this->init();
	}
	
	private function init()
	{
		$this->field = array_fill(0, 9, array_fill(0, 9, 0));
	}
	
	public function createField ()
	{
		$this->init();
		
		for ($row = 0; $row < 9; $row++)
		{
			$this->fillRow($row);
		}
	}
	
	private function fillRow($row)
	{
		$col = 0;
		
		$status = false;
		$count = 0;
		$errorOccuredAtCol = 0;
		$errorCount = 0;
		
		while ($status === false)
		{
			$possibleNumbers = $this->getPossibleNumbers($row, $col);
			
			if (count($possibleNumbers) > 0)
			{
				if ($col >= $errorOccuredAtCol)
				{
					$count = 0;
				}
				
				shuffle($possibleNumbers);
				
				$this->field[$row][$col] = $possibleNumbers[0];
				
				if ($col >= 8)
				{
					$status = true;
				}
				
				$col++;
			}
			else
			{
				$errorOccuredAtCol = $col;
				$count++;
				
				if ($col - $count < 0)
				{
					$col = 0;
					$errorCount++;
					
					if ($errorCount > 3)
					{
						for ($k = 0; $k < 9; $k++)
						{
							$this->field[$row][$k] = 0;
						}
						
						$tempRow = $row - 1 < 0 ? 0 : $row -1;
						
						$errorCount = 0;
						$this->fillRow($tempRow);
						$count = 0;
					}
				}
				else
				{
					$col -= $count;
				}
				
				$col = $col - $count < 0 ? $col = 0 : $col - $count;
				
				for ($i = $col; $i < 9; $i++)
				{
					$this->field[$row][$i] = 0;
				}
			}
		}
	}
	
	private function getPossibleNumbers ($row, $col)
	{
		$values = [];
		
		$rowValues = $this->getRowValues($row);
		
		foreach ($rowValues as $value)
		{
			$values[] = $value;
		}
		
		$colValues = $this->getColValues($col);
		
		foreach ($colValues as $value)
		{
			$values[] = $value;
		}
		
		$squareValues = $this->getSquareValues($row, $col);
		
		foreach ($squareValues as $squareValue)
		{
			$values[] = $squareValue;
		}
		
		$values = array_unique($values);
		
		$range = range(1,9);
		
		return array_diff($range, $values);
	}
	
	private function getRowValues ($row)
	{
		$values = [];
		
		for ($i = 0; $i < 9; $i++)
		{
			if ($this->field[$row][$i] !== 0)
			{
				$values[] = $this->field[$row][$i];
			}
		}
		
		return $values;
	}
	
	private function getColValues ($col)
	{
		$values = [];
		
		for ($i = 0; $i < 9; $i++)
		{
			if ($this->field[$i][$col] !== 0)
			{
				$values[] = $this->field[$i][$col];
			}
		}
		
		return $values;
	}
	
	private function getSquareValues($row, $col)
	{
		$xSquare = floor($row / 3);
		$ySquare = floor($col / 3);
		
		$square = [];
		
		for ($i = 0; $i < 3; $i++)
		{
			for ($j = 0; $j < 3; $j++)
			{
				$square[] = $this->field[$i + $xSquare * 3][$j + $ySquare * 3];
			}
		}
		
		return $square;
	}
	
	public function drawField ()
	{
		echo '<table>';
		for ($i = 0; $i < 9; $i++)
		{
			echo '<tr>';
			for ($j = 0; $j < 9; $j++)
			{
				echo '<td class="table-field">' . $this->field[$i][$j] . '</td>';
			}
			echo '</tr>';
		}
		echo '</table>';
	}
}

echo "
<style>
	table {
		border-collapse: collapse;
		border: 1px solid black;
		width: 200px;
		height: 200px;
	}
	td {
		text-align: center;
	}
	td:nth-of-type(3n + 0) {
		border-right: 1px solid black;
	}
	tr:nth-of-type(3n + 0) {
		border-bottom: 1px solid black;
	}
</style>";

$sudoku = new Sudoku;
$sudoku->createField();
$sudoku->drawField();