Alignment and performance comparisons in PHP

Permutation combination formula/permutation combination calculation formula P refers to the arrangement, from n elements to take R to arrange. Formula C refers to the combination, from n elements to take R, do not arrange, but in PHP we can use the N method to write, but each one of the performance will be different, let's take a look at it.

The requirement is this:

A combination of all possible specified lengths in the array is found, requiring no repetition.

Method One:

code 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); $temp _list1 = Getcombinati Ontostring ($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); $t = getcombinationtostring ($arr, 6); Var_dump ($t);

Execution time: 238ms.

Method Two:

The code is as follows

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);

Execution time: 710ms.