100 balls, 10 colors and 10 buckets each of whom can hold 10 balls of one or two color kind problem

index.php

<?php

// 10 buckets and 10 types of color and 100 balls
// Each color will have at least one ball.
// Each bucket can hold up to ten balls (in result).
// Place all balls in buckets so that each bucket at most containst two variants of color.

// This function should return list of buckets.
// Each bucket is a list of color ids (integers).
$scale = 10;
function distribute($balls, $scale) {
    $buckets = [];
    // YOUR CODE GOES HERE
    // Feel free to declare any helper methods if needed.
    return $buckets;
}

// HINT: use `#~ echo thisfile.php | entr -c php thisfile.php` to execute on file write.
// The stuff below is not relevant.
$data_sets = [];
$color_kinds = range(0, $scale - 1);

function color_ball(int $id): string {
    $codes = [];
    for ($i = 31; $i < 37; $i ++) $codes = array_merge($codes, ["\033[0;${i}m", "\033[1;${i}m"]);
    if ($id > count($codes) - 1) throw new Exception("too big color id given: $id");
    return $codes[$id] . "*" . "\033[0m";
}

function format_balls(array $balls) {
    $str = '';
    foreach ($balls as $ball) {
        $str .= color_ball($ball);
    }
    return $str;
}

for ($i = 0; $i < 100; $i ++) {
    $data_set = $color_kinds;
    $data_set_size = count($color_kinds);
    $max_size = $data_set_size * $scale;
    while ($data_set_size < $max_size) {
        shuffle($color_kinds);
        $data_set[] = $color_kinds[rand(0, $scale - 1)];
        $data_set_size ++;
    }
    shuffle($data_set);
    $data_sets[] = $data_set;
}

function test($original_balls, $buckets, $scale, &$bucket_nr) {
    $bucket_ctn = count($buckets);
    if ($bucket_ctn != $scale) {
        return "Expected number of buckets: $scale, got: $bucket_ctn";
    }

    $seen_balls = [];
    foreach ($buckets as $bucket_nr => $bucket) {
        $balls_in_bucket = count($bucket);
        if ($balls_in_bucket != $scale) {
            return "Expected $scale balls in bucket $bucket_nr, instead got: $balls_in_bucket";
        }

        $sorts_of_ball = count(array_unique($bucket));
        if ($sorts_of_ball > 2) {
            return "Expected number of kinds are 2 (at most) got: $sorts_of_ball in bucket $bucket_nr at scale $scale";
        }

        $seen_balls = array_merge($seen_balls, $bucket);
    }

    sort($seen_balls);
    sort($original_balls);

    if ($seen_balls !== $original_balls) {
        return "Tinkering with data set is not allowed, obviously.";
    }

    return null;
}

foreach ($data_sets as $nr => $balls) {
    echo "#$nr Given ".count($balls) . " balls:\n" . format_balls($balls) . "\n";

    $buckets = distribute($balls, $scale);
    echo "distributed as:\n";
    foreach ($buckets as $n => $bucket) {
        echo "  $n: [".format_balls($bucket)."]\n";
    }


    if ($error = test($balls, $buckets, $scale, $current)) {
        echo "Error: $error\n";
        if ($current !== null) {
            echo format_balls($buckets[$current]) . " in bucket $current is not correct\n";
        }
        break;
    }
    else {
        echo "Correct!\n\n";
    }
}

echo "\n\nfinish.";

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