Question

我需要从给定的数据集（n个数字）生成唯一的组合，每个组合包含r值。

基本上希望在PHP中实现C(n,r)=n!(r!(n−r)!)公式。

输入数据集{A，B，C，D}，需要3个值的唯一组合，如下所示：

C(n,r)=C(4,3) = 4!/(3!(4−3)!)
= 4

ABC ACD BCD BDA

（CDA，CAB，BCA等是重复的，应该从输出中截断）。

但我的代码

<?php
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 $char) {
            if($combination != $char)
            $new_combinations[] = $combination . $char;
        }
    }

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

}
?>

返回64个带有重复项的数组

{[0] =＆gt; string（3）＆＃34; aaa＆＃34; [1] =＆GT; string（3）＆＃34; aab＆＃34; [2] =＆GT;字符串（3）＆＃34; aac＆＃34; [3] =＆GT; string（3）＆＃34; aad＆＃34; [4] =＆GT; string（3）＆＃34; aba＆＃34; [5] =＆GT; string（3）＆＃34; abb＆＃34; [6] =＆GT; string（3）＆＃34; abc＆＃34; [7] =＆GT; string（3）＆＃34; abd＆＃34; [8] =＆GT; string（3）＆＃34; aca＆＃34; [9] =＆GT; string（3）＆＃34; acb＆＃34; [10] =＆GT; string（3）＆＃34; acc＆＃34; [11] =＆GT; string（3）＆＃34; acd＆＃34; [12] =＆GT; string（3）＆＃34; ada＆＃34; [13] =＆GT; string（3）＆＃34; adb＆＃34; [14] =＆GT; string（3）＆＃34; adc＆＃34; [15] =＆GT; string（3）＆＃34; add＆＃34; [16] =＆GT; string（3）＆＃34; baa＆＃34; [17] =＆GT; string（3）＆＃34; bab＆＃34; [18] =＆GT; string（3）＆＃34; bac＆＃34; [19] =＆GT; string（3）＆＃34; bad＆＃34; [20] =＆GT; string（3）＆＃34; bba＆＃34; [21] =＆GT; string（3）＆＃34; bbb＆＃34; [22] =＆GT; string（3）＆＃34; bbc＆＃34; [23] =＆GT; string（3）＆＃34; bbd＆＃34; [24] =＆GT; string（3）＆＃34; bca＆＃34; [25] =＆GT; string（3）＆＃34; bcb＆＃34; [26] =＆GT; string（3）＆＃34; bcc＆＃34; [27] =＆GT; string（3）＆＃34; bcd＆＃34; [28] =＆GT; string（3）＆＃34; bda＆＃34; [29] =＆GT; string（3）＆＃34; bdb＆＃34; [30] =＆GT; string（3）＆＃34; bdc＆＃34; [31] =＆GT; string（3）＆＃34; bdd＆＃34; [32] =＆GT; string（3）＆＃34; caa＆＃34; [33] =＆GT; string（3）＆＃34; cab＆＃34; [34] =＆GT; string（3）＆＃34; cac＆＃34; [35] =＆GT; string（3）＆＃34; cad＆＃34; [36] =＆GT; string（3）＆＃34; cba＆＃34; [37] =＆GT; string（3）＆＃34; cbb＆＃34; [38] =＆GT; string（3）＆＃34; cbc＆＃34; [39] =＆GT; string（3）＆＃34; cbd＆＃34; [40] =＆GT; string（3）＆＃34; cca＆＃34; [41] =＆GT; string（3）＆＃34; ccb＆＃34; [42] =＆GT; string（3）＆＃34; ccc＆＃34; [43] =＆GT; string（3）＆＃34; ccd＆＃34; [44] =＆GT; string（3）＆＃34; cda＆＃34; [45] =＆GT; string（3）＆＃34; cdb＆＃34; [46] =＆GT; string（3）＆＃34; cdc＆＃34; [47] =＆GT; string（3）＆＃34; cdd＆＃34; [48] =＆GT; string（3）＆＃34; daa＆＃34; [49] =＆GT; string（3）＆＃34; dab＆＃34; [50] =＆GT; string（3）＆＃34; dac＆＃34; [51] =＆GT;字符串（3）＆＃34;爸爸＆＃34; [52] =＆GT; string（3）＆＃34; dba＆＃34; [53] =＆GT; string（3）＆＃34; dbb＆＃34; [54] =＆GT; string（3）＆＃34; dbc＆＃34; [55] =＆GT; string（3）＆＃34; dbd＆＃34; [56] =＆GT; string（3）＆＃34; dca＆＃34; [57] =＆GT; string（3）＆＃34; dcb＆＃34; [58] =＆GT; string（3）＆＃34; dcc＆＃34; [59] =＆GT; string（3）＆＃34; dcd＆＃34; [60] =＆GT; string（3）＆＃34; dda＆＃34; [61] =＆GT; string（3）＆＃34; ddb＆＃34; [62] =＆GT; string（3）＆＃34; ddc＆＃34; [63] =＆GT; string（3）＆＃34; ddd＆＃34; }

提前致谢!!!

Answer 1

假设您有一组4个项目，并且您想要其中3个项目的随机子集。您可以执行以下操作：

$myset = [ "A","B","C", "D" ];    

function randomSubset($set, $size) {
    $array = array_pad(array_pad([],$size,1),count($set),0); //Get an array like [ 1,1,1,0 ];
    shuffle($array);
    return array_intersect_key($set, array_filter($array));
 }

 print_r(randomSubset($myset,3));

在沙箱中查看：http://sandbox.onlinephpfunctions.com/code/a68f3b2f1abc285424ccadbaab8a12fc4928bb8d

现在，如果你需要大小为N的所有子集，你可以做一些递归魔术：

function allSubsets($set, $size) {     
    $subsets = [];
    if ($size == 1) {
        return array_map(function ($v) { return [$v]; },$set);
    }
    foreach (allSubsets($set,$size-1) as $subset) {
        foreach ($set as $element) {
            if (!in_array($element,$subset)) {
                $newSet = array_merge($subset,[$element]);
                sort($newSet);
                if (!in_array($newSet,$subsets)) {
                    $subsets[] = array_merge($subset,[$element]);
                }
            }
        }
    }
    return $subsets;

}

 $myset = [ "A","B","C", "D", "E" ];   
 print_r(allSubsets($myset,3));

沙盒：http://sandbox.onlinephpfunctions.com/code/01b55f0c1eb55ee82a67175d2551c164ffb2bf87

Answer 2

这是一个从一组数字生成唯一组合的代码。

如果您有一组数字，例如1,3,4,7,12，则可以生成X个数字集，这些数字都是唯一的，没有重复。

第一个函数在PHP 7.4或更高版本中起作用，第二个函数使用键存储值。两者都基于基准运行良好。

function get_combos74($map, $size, &$generated = [], $loop = 1, $i = 0, $prefix = [])
{
    if ($loop == 1) {
        sort($map);
    }

    for (; $i < count($map); $i++) {
        if ($loop < $size) {
            get_combos74($map, $size, $generated, $loop + 1, $i + 1, [...$prefix, $map[$i]]);
        } else {
            $generated[] = [...$prefix, $map[$i]];
        }
    }

    return $generated;
}

function get_combosSTR($map, $size, &$generated = [], $loop = 1, $i = 0, $prefix = '')
{
    if ($loop == 1) {
        sort($map);
    }

    for (; $i < count($map); $i++) {
        if ($loop < $size) {
            get_combosSTR($map, $size, $generated, $loop + 1, $i + 1, "$prefix{$map[$i]}:");
        } else {
            $generated["$prefix{$map[$i]}"] = 0;
        }
    }

    return $generated;
}

在PHP

2 个答案: