Permutation, combination and performance comparison in PHP_PHP tutorial

Permutation, combination and performance comparison in PHP

　　Permutation and combination formula/Permutation and combination calculation formula Formula P refers to permutation, taking R elements from N elements to arrange them. Formula C refers to combination. R elements are taken from N elements without arrangement. But in PHP we can write it in N ways, but the performance of each writing method will be different. Let’s take a look below. .

The requirements are as follows:

Find all possible combinations of the specified length in the array without duplication.

Method 1:

The code is as follows

function getCombinationToString($arr,$m){ $result = array(); if ($m ==1){ return $arr; } if ($m == count($arr)){ $result[] = implode(',' , $arr); return $result; } $temp_firstelement = $arr[0]; unset($arr[0]); $arr = array_values($arr); $temp_list1 = getCombinationToString($arr, ($m-1)); foreach ($temp_list1 as $s){ $s = $temp_firstelement.','.$s; $result[] = $s; } unset($temp_list1); $temp_list2 = getCombinationToString($arr, $m); foreach ($temp_list2 as $s){ $result[] = $s; } unset($temp_list2); return $result; } $arr = array(1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18); $t = getCombinationToString($arr, 6); var_dump($t);

　　执行时间：238ms。

　　方法二：

代码如下

function getCombinAryByNum( $arr, $num,$t=array()) {
if ($num == 0) {
return array($t);
}
$r = array();
for ($i=0,$l=count($arr); $i <= $l-$num; $i++) {
$tmp = getCombinAryByNum( array_slice($arr, $i+1, $l, false), $num-1,array_merge($t, array($arr[$i])));
$r = array_merge($r, $tmp);
}
return $r;
}

代码如下

function getCombinAryByNum( $arr, $num,$t=array()) { if ($num == 0) { return array($t); } $r = array(); for ($i=0,$l=count($arr); $i <= $l-$num; $i++) { $tmp = getCombinAryByNum( array_slice($arr, $i+1, $l, false), $num-1,array_merge($t, array($arr[$i]))); $r = array_merge($r, $tmp); } return $r; } $arr = array(1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18); $numum = 6; $ss = getCombinAryByNum($arr,$numum); var_dump($ss);

$arr = array(1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18);
$numum = 6;
$ss = getCombinAryByNum($arr,$numum);

var_dump($ss);

　　执行时间：710ms。

http://www.bkjia.com/PHPjc/918724.htmlwww.bkjia.comtruehttp://www.bkjia.com/PHPjc/918724.htmlTechArticle

PHP中排列组合及性能对比 排列组合公式/排列组合计算公式公式P是指排列,从N个元素取R个进行排列。 公式C是指组合,从N个元素取R个,不进行...