Principle and application of insertion sorting method in php

This article mainly introduces the PHP insertion sort method to implement array sorting. It analyzes the principles and specific implementation techniques of the insertion sort method with examples. It has certain reference value. Friends in need can refer to this article.

The example describes how to implement array sorting using PHP insertion sort.

The specific analysis is as follows:

The basic idea of ​​insertion sorting method: also use a case to illustrate, still use $arr = array(2,6,3,9), sort from large to small .

Implementation principle: Assume (not actually created) that there is an ordered array $arr = array(2), use $arr[1]=6 to compare with it, if 6>2, by $arr[0] is moved back to the $arr[1] position, and 6 is inserted into the $arr[0] position. Then, $arr[2]=3 is compared with $arr[1]=2, 3>2, then $arr[1]=2 continues to move to the $arr[2] position, the original $arr[3]=3 Insert it into the $arr[1] position, and then continue to insert 9 into the closing position. The final result is (9,6,3,2). Sorting can also be achieved after count($arr)-1 large loops.

Code pattern analysis:

The first big loop: $[1] and $[0] ratio;
The second big loop: $[2] and $[1 ] ratio, $[1] and $[0] ratio;
The third big cycle: $[3] and $[2] ratio, $[2] and $[1] ratio, $[1] and $[0] Ratio;

PHP code uses function encapsulation to facilitate analysis using

<?php
function insertSort(&$arr){
 for($i=1;$i<count($arr);$i++){
 //$insertVal是准备插入的数
 for($j=$i;$j>0;$j--){
  if($arr[$j]>$arr[$j-1]){
  $insertVal = $arr[$j];
  $arr[$j] = $arr[$j-1];
  $arr[$j-1] = $insertVal;
  }
 }
 }
}
$myarr = array(2,6,3,9);
insertSort($myarr);
echo "<pre class="brush:php;toolbar:false">";
print_r($myarr);
?>

code:

First big loop:

$i=1 Array (2,6,3,9)
$j=1 Perform the ratio of 6 and 2: $arr[1]=2;$arr[0]=6, get (6,2 ,3,9)

Second big loop:

$i=2 Array (6,2,3,9)
$j=2 Execute ratio of 3 and 2: Become $arr[2]=2, $arr[1]=3, get (6,3,2,9)
$j--,$j=1 Execute $arr[1] and $arr[ 0] Ratio: The condition is not established

The third big loop:

$i=3 Array (6,3,2,9)
$j=3 Execute 9 and 2 ratio : Become $arr[3]=2,$arr[2]=9, get (6,3,9,2)
$j--,$j=2 Execute the ratio of 9 and 3: become $ arr[2]=3,$arr[1]=9, get (6,9,3,2)
$j--,$j=1 Execute the ratio of 9 and 6: become $arr[1] =5,$arr[0]=9, get (9,6,3,2)

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