php - PHP中特定计数的非重复组合

Question

这是一个经常重复的问题的一个特殊变体，但尽我所能，我无法在 Stack Overflow 上的任何地方找到这种确切的情况。

长话短说，我想采用这样的数组:

$days[0] = 'Monday';
$days[1] = 'Tuesday';
$days[2] = 'Thursday';

($days 可以包含一周中五个工作日的任意数量和组合。)

然后，给定 $numberOfDays 的特定值(当然，它必须至少为 1 且不超过 $days 的计数)，我想要一个包含 $days 与 $numberOfDays 天数的所有可能组合的数组。

例如:

$days[0] = 'Monday';
$days[1] = 'Tuesday';
$days[2] = 'Thursday';

$numberOfDays = 2;

$dayCombinations = getDayCombinations($days, $numberOfDays);

输出:

$dayCombinations[0] = array("Monday", "Tuesday");
$dayCombinations[1] = array("Monday", "Thursday");
$dayCombinations[2] = array("Tuesday", "Thursday");

请注意，这些是组合，而不是排列，因此顺序无关紧要。

如果有帮助，我找到了这个函数 here : 它运行良好，但包括重复，并且基于字符串而不是数组(最后一部分是可行的，没什么大不了的，但重复部分对我来说真的很糟糕)。

function sampling($chars, $size, $combinations = array()) {

    # if it's the first iteration, the first set 
    # of combinations is the same as the set of characters
    if (empty($combinations)) {
        $combinations = $chars;
    }

    # we're done if we're at size 1
    if ($size == 1) {
        return $combinations;
    }

    # initialise array to put new values in
    $new_combinations = array();

    # loop through existing combinations and character set to create strings
    foreach ($combinations as $combination) {
        foreach ($chars as $char) {
            $new_combinations[] = $combination . $char;
        }
    }

    # call same function again for the next iteration
    return sampling($chars, $size - 1, $new_combinations);
}

更新:我试图用条件来包装分配 $new_combinations 的行以提供帮助；这根本没有效果，尽管我不确定为什么。所有组合仍然存在，即使是重复的组合。

function sampling($chars, $size, $combinations = array()) {

    # if it's the first iteration, the first set 
    # of combinations is the same as the set of characters
    if (empty($combinations)) {
        $combinations = $chars;
    }

    # we're done if we're at size 1
    if ($size == 1) {
        return $combinations;
    }

    # initialise array to put new values in
    $new_combinations = array();

    # loop through existing combinations and character set to create strings
    foreach ($combinations as $combination) {
        foreach ($chars as $char) {
            if (strpos($combination, $char) === FALSE) {
                echo "Char $char not found in Combination $combination<br>";
                $new_combinations[] = $combination . $char;
            }
        }
    }

    # call same function again for the next iteration
    return sampling($chars, $size - 1, $new_combinations);
}

那里的输出返回奇怪的东西，比如:

Char 2 not found in Combination 2
Char 3 not found in Combination 23

等等。

感谢您的帮助!

亚历克斯

Answer 1

基本相同的结构，只是在添加之前检查组合中是否已经有日期。

function sampling($days, $size, $combinations = array()) {

    # if it's the first iteration, the first set 
    # of combinations is the same as the set of days
    if (empty($combinations)) {
        $combinations = array_map(function($day) { return array($day); }, $days);
    }

    # we're done if we're at size 1
    if ($size == 1) {
        return $combinations;
    }

    # initialise array to put new values in
    $new_combinations = array();

    # loop through existing combinations and character set to create strings
    foreach ($combinations as $combination) {
        foreach ($days as $day) {
            if (!in_array($day, $combination)) {
                $new_combination = $combination;
                $new_combination[] = $day;
                $new_combinations[] = $new_combination;
            }
        }
    }

    # call same function again for the next iteration
    return sampling($days, $size - 1, $new_combinations);
}

DEMO