Task: Sudoku






PHP: 	class SudokuSolver {
		protected $grid = [];
		protected $emptySymbol;
		public static function parseString($str, $emptySymbol = '0')
		{
			$grid = str_split($str);
			foreach($grid as &$v)
			{
				if($v == $emptySymbol)
				{
					$v = 0;
				}
				else
				{
					$v = (int)$v;
				}
			}
			return $grid;
		}
		
		public function __construct($str, $emptySymbol = '0') {
			if(strlen($str) !== 81)
			{
				throw new \Exception('Error sudoku');
			}
			$this->grid = static::parseString($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);
		}
	}
	$solver = new SudokuSolver('009170000020600001800200000200006053000051009005040080040000700006000320700003900');
	$solver->solve();
	$solver->display();





Fortran: program sudoku

  implicit none
  integer, dimension (9, 9) :: grid
  integer, dimension (9, 9) :: grid_solved
  grid = reshape ((/               &
    & 0, 0, 3, 0, 2, 0, 6, 0, 0,   &
    & 9, 0, 0, 3, 0, 5, 0, 0, 1,   &
    & 0, 0, 1, 8, 0, 6, 4, 0, 0,   &
    & 0, 0, 8, 1, 0, 2, 9, 0, 0,   &
    & 7, 0, 0, 0, 0, 0, 0, 0, 8,   &
    & 0, 0, 6, 7, 0, 8, 2, 0, 0,   &
    & 0, 0, 2, 6, 0, 9, 5, 0, 0,   &
    & 8, 0, 0, 2, 0, 3, 0, 0, 9,   &
    & 0, 0, 5, 0, 1, 0, 3, 0, 0/), &
    & shape = (/9, 9/),            &
    & order = (/2, 1/))
  call pretty_print (grid)
  call solve (1, 1)
  write (*, *)
  call pretty_print (grid_solved)

contains

  recursive subroutine solve (i, j)
    implicit none
    integer, intent (in) :: i
    integer, intent (in) :: j
    integer :: n
    integer :: n_tmp
    if (i > 9) then
      grid_solved = grid
    else
      do n = 1, 9
        if (is_safe (i, j, n)) then
          n_tmp = grid (i, j)
          grid (i, j) = n
          if (j == 9) then
            call solve (i + 1, 1)
          else
            call solve (i, j + 1)
          end if
          grid (i, j) = n_tmp
        end if
      end do
    end if
  end subroutine solve

  function is_safe (i, j, n) result (res)
    implicit none
    integer, intent (in) :: i
    integer, intent (in) :: j
    integer, intent (in) :: n
    logical :: res
    integer :: i_min
    integer :: j_min
    if (grid (i, j) == n) then
      res = .true.
      return
    end if
    if (grid (i, j) /= 0) then
      res = .false.
      return
    end if
    if (any (grid (i, :) == n)) then
      res = .false.
      return
    end if
    if (any (grid (:, j) == n)) then
      res = .false.
      return
    end if
    i_min = 1 + 3 * ((i - 1) / 3)
    j_min = 1 + 3 * ((j - 1) / 3)
    if (any (grid (i_min : i_min + 2, j_min : j_min + 2) == n)) then
      res = .false.
      return
    end if
    res = .true.
  end function is_safe

  subroutine pretty_print (grid)
    implicit none
    integer, dimension (9, 9), intent (in) :: grid
    integer :: i
    integer :: j
    character (*), parameter :: bar = '+-----+-----+-----+'
    character (*), parameter :: fmt = '(3 ("|", i0, 1x, i0, 1x, i0), "|")'
    write (*, '(a)') bar
    do j = 0, 6, 3
      do i = j + 1, j + 3
        write (*, fmt) grid (i, :)
      end do
      write (*, '(a)') bar
    end do
  end subroutine pretty_print

end program sudoku