Principles and usage of PHP selection sorting

This article mainly introduced the PHP choice sorting method realizes the array sorting method, the example analyzes the choice sorting principle and the concrete execution procedure, has the certain reference value, the need friend may refer to the next

In this paper, we analyze the method of sorting the array by choosing the method of PHP. Share to everyone for your reference. The specific analysis is as follows:

The basic idea of choosing a sorting method is to illustrate it directly with a case, such as an array $arr = Array (2,6,3,9), from large to small.

First big loop: It first assumes $arr[0] is the maximum value, then compares it with $arr[1]~ $arr [3], and if it is larger, it is exchanged, the process is such (2,6,3,9)---2 and 6 than---> (6,2,3,9)---6 and 3--- > (6,2,3,9)---6 and 9 than---> (9,2,3,6). Note that the subscript here also needs to change.

Second big cycle: assuming $arr[1] Max (excluding $arr[0]), compared with $arr[2]~ $arr [3], the process is such (9,2,3,6)----2 and 3 than----> (9,3,2,6)---3 and 6 than---> ( 9,6,2,3).

The third big cycle: assuming $arr[2] max, compared to $arr[3], the process is like this (9,6,2,3)---2 and 3 than---> (9,6,3,2)

In the same way, after N-1 cycles, you can arrange them.

The PHP code is as follows, and here is the same wrapper with the function

<?phpfunction selectsort (& $arr) {for ($i =0; $i <count ($arr); $i + +) {$max = $arr [$i]; for ($j = $i +1; $j <count ($ ARR), $j + +) {  if ($max < $arr [$j]) {  $max = $arr [$j];  $arr [$j] = $arr [$i];  $arr [$i] = $max;  } }} return $arr;} $myarr = Array (2,6,3,9); Selectsort ($myarr); echo "<pre>";p Rint_r ($myarr);? >

Code Analysis:

First big cycle:

$i =0 Array (2,6,3,9)
$j = 1, performs 2 and 6 ratios: becomes $arr[0]=6, $arr [1]=2, $max =6 (6,2,3,9)
$j = 2, perform 3 and 6 ratio: do not execute
$j = 3, performs 9 and 6 ratios: becomes $arr[0]=9, $arr [3]=6, $max =9 (9,2,3,6)

Second big cycle:

$i =1, $max = $arr [1]=2, Array (9,2,3,6)
$j = 2, performs 3 and 2 ratios: becomes $arr[1]=3, $arr [2]=2, $max =3 (9,3,2,6)
$j = 3, performs 6 and 3 ratios: becomes $arr[1]=6, $arr [3]=3, $max =6 (9,6,2,3)

The third big cycle:

$i =2, $max = $arr [2]=2, Array (9,6,2,3)
$j = 3, performs 3 and 2 ratios: becomes $max[2]=3, $arr [3]=2, $max =3 (9,6,3,2)

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