Commonly used bubble sorting & quick sorting algorithms and binary search & sequential search algorithm implementation in PHP

The content this article brings to you is about the commonly used bubble sorting & quick sorting algorithm and binary search & sequential search algorithm implementation in PHP. It has certain reference value. Friends in need can refer to it. I hope It will help you.

1. Bubble sorting

Basic idea:

Sort the array from back to front (reverse order) Perform multiple scans, and when it is found that the order of two adjacent values ​​​​is inconsistent with the rules required for sorting, the two values ​​​​are exchanged. In this way, the smaller (larger) values ​​will gradually move from the back to the front.

<?php
function mysort($arr)
{
for($i = 0; $i < count($arr); $i++)
{
$isSort = false;
for ($j=0; $j< count($arr) - $i - 1; $j++) 
{
if($arr[$j] < $arr[$j+1])
{
$isSort = true;
$temp = $arr[$j];
$arr[$j] = $arr[$j+1];
$arr[$j+1] = $temp ;
}
}
if($isSort)
{
break;
}
}
return $arr;
}
$arr = array(3,1,2);
var_dump(mysort($arr));
?>

2. Quick sort

Basic idea:

Select an element in the array (mostly the first ) as the ruler, scan the array once and sort the elements smaller than the ruler before the ruler, sort all the elements larger than the ruler after the ruler, and divide each subsequence into smaller sequences through recursion until all the sequences are in the same order. .

<?php
//快速排序
function quick_sort($arr) 
{
//先判断是否需要继续进行
$length = count($arr);
if($length <= 1) 
{
return $arr;
}
$base_num = $arr[0];//选择一个标尺 选择第一个元素
//初始化两个数组
$left_array = array();//小于标尺的
$right_array = array();//大于标尺的
for($i=1; $i<$length; $i++) 
{      //遍历 除了标尺外的所有元素，按照大小关系放入两个数组内
if($base_num > $arr[$i]) 
{
//放入左边数组
$left_array[] = $arr[$i];
} 
else
{
//放入右边
$right_array[] = $arr[$i];
}
}
//再分别对 左边 和 右边的数组进行相同的排序处理方式
//递归调用这个函数,并记录结果
$left_array = quick_sort($left_array);
$right_array = quick_sort($right_array);
//合并左边 标尺 右边
return array_merge($left_array, array($base_num), $right_array);
}
$arr = array(3,1,2);
var_dump(quick_sort($arr));
?>

Three, binary search

Basic idea:

Assume that the data is sorted in ascending order, for a given value x, starting from the middle position of the sequence, if the current position value is equal to x, the search is successful; if x is less than the current position value, the search is in the first half of the sequence; if x is greater than the current position value, the search is in the second half of the sequence Keep searching until you find it. (Use when the amount of data is large)

<?php
//二分查找
function bin_search($arr,$low,$high,$k)
{
 if($low <= $high)
{
$mid = intval(($low + $high)/2);
if($arr[$mid] == $k)
{
return $mid;
}
else if($k < $arr[$mid])
{
return bin_search($arr,$low,$mid-1,$k);
}
else
{
return bin_search($arr,$mid+1,$high,$k);
}
}
 return -1;
}
$arr = array(1,2,3,4,5,6,7,8,9,10);
print(bin_search($arr,0,9,3));
?>

4. Sequential search

Basic idea:

Start from the first position of the array An element is searched downwards one by one. If there is an element consistent with the target, the search is successful; if there is still no target element until the last element, the search fails.

<?php
//顺序查找
function seq_search($arr,$n,$k)
{
$array[$n] = $k;
for($i = 0;$i < $n; $i++)
{
if($arr[$i] == $k)
 {
break;
}
if($i < $n)
{
return $i;
}
else
{
return -1;
}
}
?>

5. Write a function that can traverse all files and subfolders under a file

<?php  
function my_scandir($dir)
{
$files = array();
if($handle = opendir($dir))
{
while (($file = readdir($handle))!== false) 
{
if($file != &#39;..&#39; && $file != &#39;.&#39;)
{
if(is_dir($dir."/".$file))
{
$files[$file]=my_scandir($dir."/".$file);
}
else
{
$files[] = $file;
}
}
}
closedir($handle);
return $files;
}
}
var_dump(my_scandir(&#39;../&#39;));
?>		

6. Write a function that is as efficient as possible Get the file extension from a standard url

<?php
function getExt($url)
{
$arr = parse_url($url);//parse_url解析一个 URL 并返回一个关联数组，包含在 URL 中出现的各种组成部分
//&#39;scheme&#39; => string &#39;http&#39; (length=4)
//&#39;host&#39; => string &#39;www.sina.com.cn&#39; (length=15)
//&#39;path&#39; => string &#39;/abc/de/fg.php&#39; (length=14)
//&#39;query&#39; => string &#39;id=1&#39; (length=4)
$file = basename($arr[&#39;path&#39;]);// basename函数返回路径中的文件名部分
$ext = explode(&#39;.&#39;, $file);
 return $ext[count($ext)-1];
}
print(getExt(&#39;http://www.sina.com.cn/abc/de/fg.html.php?id=1&#39;));
?>

7. Method to intercept Chinese string without garbled characters

You can use mb_substr, but you need to ensure php_mbstring.dll is loaded in php.ini, that is, ensure that the line "extension=php_mbstring.dll" exists and is not commented out, otherwise undefined function problems will occur.

Related recommendations:

PHP implements bubble sorting, php bubble sorting

Bubble sorting in php, Rounding sort, insertion sort

The above is the detailed content of Commonly used bubble sorting & quick sorting algorithms and binary search & sequential search algorithm implementation in PHP. For more information, please follow other related articles on the PHP Chinese website!