Question

I have an array of part lengths, for examples sake:-

array(150, 180, 270);

I then have a measurement ($a = 440)

I need to calculate the two closest possible combinations of lengths which are greater than $a without manually having to write hundreds of possible combinations in order to work it out.

So:

150
180
270

150 + 150
150 + 180
150 + 270

180 + 180
180 + 270

270 + 270

150 + 150 + 150
150 + 150 + 180

..and so on.

This will need to run for a set number of times, rather than just finding the first two matches and stopping, as 150 + 150 + 150 would be a closer match to $a than 270 + 270 but may run after.

edit: I also need to store the combination of parts which made up the match, preferably in an array.

I hope I’ve explained this well enough for somebody to understand.

Answer 1

As this is quite a resource heavy script, I thought it would be a good idea to give the option to generate the choices beforehand, then use that data to create a variable/object/sql script to permanently store the data. For instance, doing something like

SELECT * FROM combination_total WHERE size > YOUR_SIZE ORDER BY size ASC LIMIT 2;

The new script I have is similar, but it just generates an array of all combinations without any duplicates. Seems pretty quick again. Notice the $maxLength variable, which is currently set to 2000, which can be modified with your own largest possible size.

<?php
$partLengths = array(150, 180, 270);
$currentCombinations = array(
    array(
        'total' => 150,
        'combination' => array(150)
    ),
    array(
        'total' => 180,
        'combination' => array(180)
    ),
    array(
        'total' => 270,
        'combination' => array(270)
    )
);
$maxLength = 2000;
$largestSize = 0;

function generateCombination() {
    global $currentCombinations, $largestSize, $partLengths;
    $tmpCombinations = $currentCombinations;
    foreach ($tmpCombinations as $combination) {
        foreach ($partLengths as $partLength) {
            $newCombination = $combination['combination'];
            $newCombination[] = $partLength;
            sort($newCombination);

            $newCombinationTotal = array_sum($newCombination);

            if (!combinationExists($newCombination)) {
                $currentCombinations[] = array(
                        'total' => $newCombinationTotal,
                        'combination' => $newCombination
                );
            }

            $largestSize = ($newCombinationTotal > $largestSize) ? $newCombinationTotal : $largestSize;
        }
    }
}

function combinationExists($combination) {
    global $currentCombinations;
    foreach ($currentCombinations as $currentCombination) {
        if ($combination == $currentCombination['combination']) {
            return true;
        }
    }
    return false;
}

while ($largestSize < $maxLength) {
    generateCombination();
}

// here you can use $currentCombinations to generate sql/object/etc
var_dump($currentCombinations);
?>