Sudoku

    /**
    * Method to add puzzle
    * puzzle generated using the "Peraita method - Author unknown"
    * @param string $difficulty The difficulty raing of the puzzle (used to remove numbers)
    * $size the base size of the grid eg. 3 = 9x9 board, 5 = 25*25 board
    **/
    function generate($difficulty)
    {
        // set up board size
        if($difficulty != 4){
            $size = 3;
        }else{
            $size = 5;
        }
        // randomize numbers
        $numbers = range(1, pow($size, 2));
        shuffle($numbers);

        // row index sets
        $x = 1;
        for($i = 1; $i <= pow($size, 2); $i++){
            $a = "rowIndex_" . $i; //set up variable names eg $rowIndex_1
            for($ii = 1; $ii <= pow($size, 2); $ii++){
                ${$a}[$ii] = $x; //set up variable eg $rowIndex[0] = 1
                $x = $x + 1;
            }
            $allRows[$i] = $$a; //set up array eg $temp[0] = $rowIndex_1
        }
        $temp = array_chunk($allRows, $size, true);
        foreach($temp as $key => $arrRow){
            $a = "arrRow_" . $key; // set up variable names
            $$a = $arrRow; // set up variable
            $arrAllRows[$key] = $$a; // set up array
        }

        // column index sets
        for($i = 1; $i <= pow($size, 2); $i++){
            $a = "colIndex_" . $i; // set up variable names
            $x = $i;
            for($ii = 1; $ii <= pow($size, 2); $ii++){
                ${$a}[$ii] = $x; // set up variable
                $x = $x + pow($size, 2);
            }
            $allCols[$i] = $$a; // set up array
        }
        $temp = array_chunk($allCols, $size, true);
        foreach($temp as $key => $arrCol){
            $a = "arrCol_" . $key; // set up variable names
            $$a = $arrCol;  // set up variable
            $arrAllCols[$key] = $$a; // set up array
        }

        // block index sets
        $x = 1;
        $y = 1;
        for($i = 1; $i <= $size; $i++){
            for($ii = 1; $ii <= $size; $ii++){
                $a = "blockIndex_" . $x; // set up variable names
                $z = 1;
                for($iii = 1; $iii <= $size; $iii++){
                    for($iv = 1; $iv <= $size; $iv++){
                        ${$a}[$z++] = $y; // set up variable
                        $y = $y + 1;
                    }
                    $y = $y + ((pow($size, 2)) - ($size));
                }
                $arrAllBlocks[$x] = $$a; // set up array
                $x = $x + 1;
            }
            $y = ($i * $size) + 1;
        }

        // set up basic board
        for($i = 1; $i <= pow($size, 2); $i++){
            foreach($arrAllBlocks as $block){
                $temp = $numbers;
                foreach($block as $index){
                    $data[$index] = array_shift($temp);
                }
                $firstNumber = array_shift($numbers);
                $numbers = array_pad($numbers, pow($size, 2), $firstNumber);
            }
        }
        ksort($data);

        // shuffle rows
        for($i = 0; $i <= $size - 2; $i++){
            foreach($arrAllRows as $arrRows){
                shuffle($arrRows);
                $arrRows = array_slice($arrRows, 0, 2); // takes first 2 rows
                foreach($arrRows as $key => $row){
                    foreach($row as $rowKey => $index){
                        if($key == 0){
                            $row_1[$rowKey] = $data[$index];
                        }else{
                            $row_2[$rowKey] = $data[$index];
                        }
                    }
                }
                foreach($arrRows as $key => $row){ // swops them
                    foreach($row as $rowKey => $index){
                        if($key == 0){
                            $data[$index] = $row_2[$rowKey];
                        }else{
                            $data[$index] = $row_1[$rowKey];
                        }
                    }
                }
            }
        }

        // shuffle columns
        for($i = 0; $i <= $size - 2; $i++){
            foreach($arrAllCols as $arrCols){
                shuffle($arrCols);
                $arrCols = array_slice($arrCols, 0, 2); // takes first 2 columns
                foreach($arrCols as $key => $col){
                    foreach($col as $colKey => $index){
                        if($key == 0){
                            $col_1[$colKey] = $data[$index];
                        }else{
                            $col_2[$colKey] = $data[$index];
                        }
                    }
                }
                foreach($arrCols as $key => $col){ // swops them
                    foreach($col as $colKey => $index){
                        if($key == 0){
                            $data[$index] = $col_2[$colKey];
                        }else{
                            $data[$index] = $col_1[$colKey];
                        }
                    }
                }
            }
        }
        $solution = implode(",", $data);

        //remove pairs of numbers symetrically
        if($difficulty == 1){
            $pairs = 16;
        }elseif($difficulty == 2){
            $pairs = 22;
        }elseif($difficulty == 3){
            $pairs = 30;
        }else{
            $pairs = 170;
        }
        for($i = 1; $i <= $pairs; $i++){
            do{
                $number_1 = rand(1, pow($size, 4));
            }while($number_1 == (((pow($size, 4) - 1) / 2) + 1));
            $data[$number_1] = '';
            $number_2 = (pow($size, 4) + 1) - $number_1;
            $data[$number_2] = '';
        }
        
        $puzzle = implode(",", $data);
    }