PHP arrays - unique combinations out of 3 arrays

Question

I'm not even sure how to approach the problem so I'm just stating the problem. Any help is highly appreciated.

There's this array ($colors) of all possible values:

$colors = array ('red','blue','green','yellow');

Then there's an array ($boxes) of all the possible values - consisting of equal number of values as $colors:

$boxes = array ('circular','squared','hexagonal','triangular');

There's this third array which defines the constraints in making the unique combination:

$possible_combos = array  
(  
array('circular','red','blue'),  
array('squared','red','green'),
array('hexagonal','blue','yellow'),
array('triangular','red','green')
);

Question: How do I get a new array $result with key=>value combinations just that each box is assigned a unique color out of it's possible sets of colors

So a valid $result array would be:

Array ( [circular] => red 
        [squared]  => blue 
        [hexagonal]=> yellow
        [triangular] => green
      ) 

NOTE: If you traverse sequentially, 'red', 'blue', 'green' might get assigned to first three 'boxes' and there might not be anything to pick for the fourth box (since 'yellow' is not allowed to be assigned to it.
I'm thinking, to process the least occurring 'colors' first but really unsure how to handle it syntactically.

Once again thanks for looking into it, in advance! Even some help with how to approach the problem would be nice.

Following code is not producing the correct output either:

foreach ($colors as $c => $color) {
    foreach ($boxes as $b => $box) {
        for ($i=0; $i < count($colors) ; $i++) {
            if(in_array($possible_combos[$i][1],$colors) && !in_array($possible_combos[$i][1], $result))
            {
                $result[$box] = $possible_combos[$i][1];
                unset($colors[$c]);
                break;
            }
            else if(in_array($possible_combos[$i][2],$colors) && !in_array($possible_combos[$i][2], $result))
            {
                $result[$box] = $possible_combos[$i][2];
                unset($colors[$c]);
                break;
            }
        }
    }
}

Answer 1

I'm thinking, to process the least occurring 'colors' first but really unsure how to handle it syntactically.

That's a good intuition considering the fact that you have only one box type that can share one of many colors. Because your constraining resource is color, I think it makes sense to sort your rules by them first and then you can distribute by scarcity.

https://3v4l.org/u5pBK

$colors = array ('red','blue','green','yellow');

$boxes = array ('circular','squared','hexagonal','triangular');

$possible_combos = array
(
    array('circular','red','blue'),
    array('squared','red','green'),
    array('hexagonal','blue','yellow'),
    array('triangular','red','green')
);

// collect constraints ordered by rarest
foreach ($possible_combos as $constraint) {
    $box = array_shift($constraint);
    foreach ($constraint as $color) {
        $constraints[$color] []= $box;
    }
}

// assign rarest first to last
asort($constraints);
foreach ($constraints as $color => $allowedBoxes) {
    foreach ($allowedBoxes as $box) {
        $key = array_search($box, $boxes);
        // if we have a match, then remove it from the collection
        if ($key !== false) {
            $result[$box] = $color;
            unset($boxes[$key]);
            continue 2;
        }
    }
}

print_r($result);

Array
(
    [hexagonal] => yellow
    [circular] => blue
    [squared] => green
    [triangular] => red
)