Algoritimo que gera uma grade de sudoku válida em PHP

sudoku

<?php

function return_row($cell){
	return floor($cell/9);
}

function return_col($cell){
	return $cell % 9;
}

function return_block($cell){
	return floor(return_row($cell)/3)*3+floor(return_col($cell)/3);
}

function is_possible_row($number,$row,$sudoku){
	$possible = true;
	for($x=0;$x<=8;$x++){		
		if($sudoku[$row*9+$x] == $number){
			$possible = false;
		}		
	}
	return $possible;
}

function is_possible_col($number,$col,$sudoku){
	$possible = true;
	for($x=0;$x<=8;$x++){
		if($sudoku[$col+9*$x] == $number){
			$possible = false;
		}
	}
	return $possible;
}

function is_possible_block($number,$block,$sudoku){
	$possible = true;
	for($x=0;$x<=8;$x++){
		if($sudoku[floor($block/3)*27+$x%3+9*floor($x/3)+3*($block%3)] == $number){
			$possible = false;
		}
	}
	return $possible;
}
 
function is_possible_number($cell,$number,$sudoku){
	$row = return_row($cell);
	$col = return_col($cell);
	$block = return_block($cell);
	return is_possible_row($number,$row,$sudoku) and is_possible_col($number,$col,$sudoku) and is_possible_block($number,$block,$sudoku);
}	
 
function print_sudoku($sudoku){
	$html = "<table bgcolor = \"#000000\" cellspacing = \"1\" cellpadding = \"2\">";
	for($x=0;$x<=8;$x++){
		$html .= "<tr bgcolor = \"white\" align = \"center\">";
		for($y=0;$y<=8;$y++){
			$html.= "<td width = \"25\" height = \"25\">".$sudoku[$x*9+$y]."</td>";
		}
		$html .= "</tr>";
	}
	$html .= "</table>";
	return $html;
}
 
function is_correct_row($row,$sudoku){
	for($x=0;$x<=8;$x++){
		$row_temp[$x] = $sudoku[$row*9+$x];
	}
	return count(array_diff(array(1,2,3,4,5,6,7,8,9),$row_temp)) == 0;
}
 
 
 
function is_correct_col($col,$sudoku){
	for($x=0;$x<=8;$x++){
		$col_temp[$x] = $sudoku[$col+$x*9];
	}
	return count(array_diff(array(1,2,3,4,5,6,7,8,9),$col_temp)) == 0;
}
 
function is_correct_block($block,$sudoku){
	for($x=0;$x<=8;$x++){
		$block_temp[$x] = $sudoku[floor($block/3)*27+$x%3+9*floor($x/3)+3*($block%3)];
	}
	return count(array_diff(array(1,2,3,4,5,6,7,8,9),$block_temp)) == 0;
}
 
function is_solved_sudoku($sudoku){
	for($x=0;$x<=8;$x++){
		if(!is_correct_block($x,$sudoku) or !is_correct_row($x,$sudoku) or !is_correct_col($x,$sudoku)){
			return false;
			break;
		}
	}
	return true;
}
 
function determine_possible_values($cell,$sudoku){
	$possible = array();
	for($x=1;$x<=9;$x++){
		if(is_possible_number($cell,$x,$sudoku)){
			array_unshift($possible,$x);
		} 
	}
	return $possible;
}
 
function determine_random_possible_value($possible,$cell){
	return $possible[$cell][rand(0,count($possible[$cell])-1)];
}
 
function scan_sudoku_for_unique($sudoku){
	for($x=0;$x<=80;$x++){
		if($sudoku[$x] == 0){
			$possible[$x] = determine_possible_values($x,$sudoku);
			if(count($possible[$x])==0){
				return(false);
				break;
			}
		}
	}
	return($possible);
}
 
function remove_attempt($attempt_array,$number){
	$new_array = array();
	for($x=0;$x<count($attempt_array);$x++){
		if($attempt_array[$x] != $number){
			array_unshift($new_array,$attempt_array[$x]);
		}
	}
	return $new_array;
}
 
 
function print_possible($possible){
	$html = "<table bgcolor = \"#ff0000\" cellspacing = \"1\" cellpadding = \"2\">";
	for($x=0;$x<=8;$x++){
		$html .= "<tr bgcolor = \"yellow\" align = \"center\">";
		for($y=0;$y<=8;$y++){
			$values = "";
			for($z=0;$z<=count($possible[$x*9+$y]);$z++){
				$values .= $possible[$x*9+$y][$z];
			}
			$html.= "<td width = \"25\" height = \"25\">$values</td>";
		}
		$html .= "</tr>";
	}
	$html .= "</table>";
	return $html;
}	
 
function next_random($possible){
	$max = 9;
	for($x=0;$x<=80;$x++){
		if ((count($possible[$x])<=$max) and (count($possible[$x])>0)){
			$max = count($possible[$x]);
			$min_choices = $x;
		}
	}
	return $min_choices;
}
 
 
function solve($sudoku){
	$start = microtime();
	$saved = array();	
	$saved_sud = array();
	while(!is_solved_sudoku($sudoku)){
		$x+=1;
		$next_move = scan_sudoku_for_unique($sudoku);
		if($next_move == false){
			$next_move = array_pop($saved);
			$sudoku = array_pop($saved_sud);
		}
		$what_to_try = next_random($next_move);	
		$attempt = determine_random_possible_value($next_move,$what_to_try);
		if(count($next_move[$what_to_try])>1){					
			$next_move[$what_to_try] = remove_attempt($next_move[$what_to_try],$attempt);
			array_push($saved,$next_move);
			array_push($saved_sud,$sudoku);
		}
		$sudoku[$what_to_try] = $attempt;	
	}
	$end = microtime();
	$ms_start = explode(" ",$start);
	$ms_end = explode(" ",$end);
	$total_time = round(($ms_end[1] - $ms_start[1] + $ms_end[0] - $ms_start[0]),2);
	echo "completed in $x steps in $total_time seconds";
	echo print_sudoku($sudoku);
}
 
$sudoku = array(0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0);
 
solve($sudoku);
?><br>
I'm the like a boss :)