36 cube iterative solution FULL

<?php

$colors = array(
     1 => 'R',
     2 => 'O',
     4 => 'Y',
     8 => 'G',
    16 => 'B',
    32 => 'P',
    false => 'X',
);

$used_towers = array_fill(0, 6, 0);

$cube = array(
    array(1,3,4,5,2,0),
    array(2,5,1,4,1,3),
    array(0,1,3,2,5,4),
    array(5,4,0,3,0,2),
    array(4,2,5,0,3,1),
    array(3,0,2,1,4,5),
);

$solution = array_fill(0, 6, array_fill(0, 6, false));
$solutions = array( );

function test_color($pos, $solution, $used_towers, $color, $size) {
    if (36 <= $pos) {
        return false;
    }

    // check if piece exists in solution at this location
    if (false !== $solution[floor($pos / 6)][$pos % 6]) {
        return false;
    }

    // check if tower of this size and color has already been used
    if ($color & $used_towers[$size]) {
        return false;
    }

    // check if tower has already been used in row or column:
    for ($i = 0; $i < 6; ++$i) {
        if ($color == $solution[floor($pos / 6)][$i]) {
            return false;
        }

        if ($color == $solution[$i][$pos % 6]) {
            return false;
        }
    }

    // special conditions for the two special towers
    if (array(1, 2) == (array(floor($pos / 6), $pos % 6)) && (4 != $color)) {
        return false;
    }

    if (array(3, 2) == (array(floor($pos / 6), $pos % 6)) && (2 != $color)) {
        return false;
    }

    return true;
}


function filter_color($used, $color) {
    foreach ($used as & $row) {
        $row = (bool) ($color & $row);
    }
    unset($row);

    return array_filter($used);
}


function solve_color_by_pieces($color, $solution, $used_towers, $continue_colors = false) {
    global $colors, $cube, $MASTER;

    $orig = $solution;

    if (32 < $color) {
        // convert all numbers to letters based on position and flatten
        list($converted, $key) = convert_solution($solution);
        if ( ! in_array($converted, $MASTER['solution'])) {
            $MASTER['solution'][] = $converted;
            $MASTER['key'][] = $key;
        }

        return $solution;
    }

    if (6 <= count(filter_color($used_towers, $color))) {
        return solve_color_by_pieces($color << 1, $solution, $used_towers, $continue_colors);;
    }

    $sols = array( );
    $size = 0;

    while (5 >= $size) {
        if ($color & $used_towers[$size]) {
            $size++;
            continue;
        }

        // find ALL possible solutions for this size
        for ($pos = 0; $pos < 36; ++$pos) {
            if ($size != $cube[floor($pos / 6)][$pos % 6]) {
                continue;
            }

            if ( ! test_color($pos, $solution, $used_towers, $color, $size)) {
                continue;
            }

            // add to this solution path and continue...
            $solution[floor($pos / 6)][$pos % 6] = $color;
            $used_towers[$size] |= $color;

            // if we're not done with this color
            if (6 > count(filter_color($used_towers, $color))) {
                $return = solve_color_by_pieces($color, $solution, $used_towers, $continue_colors);
            }
            elseif ($continue_colors) {
                $return = solve_color_by_pieces($color << 1, $solution, $used_towers, $continue_colors);
            }
            else {
                $return = $solution;
            }

            if ($return) {
                $sols[] = $return;
            }

            // remove this solution and continue searching this level
            $solution[floor($pos / 6)][$pos % 6] = false;
            $used_towers[$size] ^= $color;
        }

        break;
    }

    return $sols;
}


function convert_solution($sol) {
    global $colors;

    $letters = array('A','B','C','D','E','F');

    $output = '';
    foreach ($sol as $i => & $row) {
        foreach ($row as $j => & $piece) {
            if ( ! $i) {
                $conv[$piece] = $letters[$j];
            }
            $output .= $conv[$piece];
        }
    }

    $key = array( );
    foreach ($conv as $color => $letter) {
        $key[$letter] = $colors[$color];
    }

    return array($output, $key);
}

// solve for red
$solution[1][2] = 4; // yellow
$size = $cube[1][2];
$used_towers[$size] |= 4;

$solution[3][2] = 2; // orange
$size = $cube[3][2];
$used_towers[$size] |= 2;
$color = 1;

$MASTER = array('solution' => array( ), 'key' => array( ));

solve_color_by_pieces($color, $solution, $used_towers, true);
debug($MASTER);



/** function call [dump] [debug]
 *      This function is for debugging only
 *      Outputs given var to screen
 *      or, if no var given, outputs stars to note position
 *
 * @param mixed optional var to output
 * @param bool optional bypass debug value and output anyway
 * @action outputs var to screen
 * @return void
 */
function call($var = 'Th&F=xUFucreSp2*ezAhe=ApuPR*$axe', $bypass = false, $show_from = true, $new_window = false, $error = false)
{
    if ((( ! defined('DEBUG') || ! DEBUG) || ! empty($GLOBALS['NODEBUG'])) && ! (bool) $bypass) {
        return false;
    }

    if ('Th&F=xUFucreSp2*ezAhe=ApuPR*$axe' === $var) {
        $contents = '<span style="font-size:larger;font-weight:bold;color:red;">--==((OO88OO))==--</span>';
    }
    else {
        // begin output buffering so we can escape any html
        // and print_r is better at catching recursion than var_export
        ob_start( );

        if ((is_string($var) && ! preg_match('/^\\s*$/', $var))) { // non-whitespace strings
            print_r($var);
        }
        else {
            if ( ! function_exists('xdebug_disable')) {
                if (is_array($var) || is_object($var)) {
                    print_r($var);
                }
                else {
                    var_dump($var);
                }
            }
            else {
                var_dump($var);
            }
        }

        // end output buffering and output the result
        if ( ! function_exists('xdebug_disable')) {
            $contents = htmlentities(ob_get_contents( ));
        }
        else {
            $contents = ob_get_contents( );
        }

        ob_end_clean( );
    }

    $j = 0;
    $html = '';
    $debug_funcs = array('dump', 'debug');
    if ((bool) $show_from) {
        $called_from = debug_backtrace( );

        if (isset($called_from[$j + 1]) && in_array($called_from[$j + 1]['function'], $debug_funcs)) {
            ++$j;
        }

        $file0 = substr($called_from[$j]['file'], strlen($_SERVER['DOCUMENT_ROOT']));
        $line0 = $called_from[$j]['line'];

        $called = '';
        if (isset($called_from[$j + 1]['file'])) {
            $file1 = substr($called_from[$j + 1]['file'], strlen($_SERVER['DOCUMENT_ROOT']));
            $line1 = $called_from[$j + 1]['line'];
            $called = "{$file1} : {$line1} called ";
        }
        elseif (isset($called_from[$j + 1]['class'])) {
            $called = $called_from[$j + 1]['class'].$called_from[$j + 1]['type'].$called_from[$j + 1]['function'].' called ';
        }

        $html = "<strong>{$called}{$file0} : {$line0}</strong>\n";
    }

    if ( ! $new_window) {
        $color = '#000';
        if ($error) {
            $color = '#F00';
        }

        echo "\n\n<pre style=\"background:#FFF;color:{$color};font-size:larger;\">{$html}{$contents}\n<hr /></pre>\n\n";
    }
    else { ?>
        <script language="javascript">
            myRef = window.open('','debugWindow');
            myRef.document.write('\n\n<pre style="background:#FFF;color:#000;font-size:larger;">');
            myRef.document.write('<?php echo str_replace("'", "\'", str_replace("\n", "<br />", "{$html}{$contents}")); ?>');
            myRef.document.write('\n<hr /></pre>\n\n');
        </script>
    <?php }
}
function dump($var = 'Th&F=xUFucreSp2*ezAhe=ApuPR*$axe', $bypass = false, $show_from = true, $new_window = false, $error = false) { call($var, $bypass, $show_from, $new_window, $error); }
function debug($var = 'Th&F=xUFucreSp2*ezAhe=ApuPR*$axe', $bypass = true, $show_from = true, $new_window = false, $error = false) { call($var, $bypass, $show_from, $new_window, $error); }