grid = static::parseString($str, $emptySymbol);
$this->emptySymbol = $emptySymbol;
}
public function solve()
{
try {
$this->placeNumber(0);
return false;
} catch (\Exception $e) {
return true;
}
}
protected function placeNumber($pos)
{
if ($pos == 81) {
throw new \Exception("Finish");
}
if ($this->grid[$pos] > 0) {
$this->placeNumber($pos + 1);
return;
}
for ($n = 1; $n <= 9; $n++) {
if ($this->checkValidity($n, $pos % 9, floor($pos / 9))) {
$this->grid[$pos] = $n;
$this->placeNumber($pos + 1);
$this->grid[$pos] = 0;
}
}
}
protected function checkValidity($val, $x, $y)
{
for ($i = 0; $i < 9; $i++) {
if (($this->grid[$y * 9 + $i] == $val) || ($this->grid[$i * 9 + $x] == $val)) {
return false;
}
}
$startX = (int) ((int) ($x / 3) * 3);
$startY = (int) ((int) ($y / 3) * 3);
for ($i = $startY; $i < $startY + 3; $i++) {
for ($j = $startX; $j < $startX + 3; $j++) {
if ($this->grid[$i * 9 + $j] == $val) {
return false;
}
}
}
return true;
}
public function display()
{
$str = "";
for ($i = 0; $i < 9; $i++) {
for ($j = 0; $j < 9; $j++) {
$str .= $this->grid[$i * 9 + $j];
$str .= " ";
if ($j == 2 || $j == 5) {
$str .= "| ";
}
}
$str .= PHP_EOL;
if ($i == 2 || $i == 5) {
$str .= "------+-------+------" . PHP_EOL;
}
}
echo $str;
}
public function __toString()
{
foreach ($this->grid as &$item) {
if ($item == 0) {
$item = $this->emptySymbol;
}
}
return implode("", $this->grid);
}
}
?>
Solve Sudoku (Made by MiTiX)
solve();
$output = (string) $solver;
?>
Made by @MiTiX
source: https://rosettacode.org/wiki/Sudoku
source: https://gist.github.com/thebinarypenguin/4d45ffe87096e508800b5d11544bf2fa