Detailed explanation of four basic PHP algorithms
This article mainly shares with you the detailed explanation of four basic PHP algorithms. Randomly select 100 numbers from 1 to 1000, and use bubble sort, quick sort, selection sort, and insertion sort to combine the values in the array below. Sort in order from smallest to smallest.
Solution:
0. Randomly pick 100 numbers from 1 to 1000 and store them in the array.
$arr = array();
//生成100个元素的数组
for ($i=0; $i < 100; $i++) {
$a = rand(1,1000);
array_push($arr, $a);
}1. Bubble sorting method
* Idea analysis: The method is as its name suggests, just like bubbling, the largest number emerges from the array each time.
* For example: 2,4,1 // The first bubble is 4
* 2,1,4 // The second bubble is 2
function bubble_sort(&$arr) {
$len=count($arr);
//设置一个空数组 用来接收冒出来的泡
//该层循环控制 需要冒泡的轮数
for($i=1;$i<$len;$i++)
{ //该层循环用来控制每轮 冒出一个数 需要比较的次数
for($k=0;$k<$len-$i;$k++)
{
if($arr[$k]>$arr[$k+1])
{
$tmp=$arr[$k+1];
$arr[$k+1]=$arr[$k];
$arr[$k]=$tmp;
}
}
}
return $arr;
}2. Selection sorting method:
Selection sorting method idea: Select a corresponding element each time and then place it in the specified position.
function select_sort(&$arr) {
//实现思路 双重循环完成，外层控制轮数，当前的最小值。内层 控制的比较次数
//$i 当前最小值的位置， 需要参与比较的元素
for($i=0, $len=count($arr); $i<$len-1; $i++) {
//先假设最小的值的位置
$p = $i;
//$j 当前都需要和哪些元素比较，$i 后边的。
for($j=$i+1; $j<$len; $j++) {
//$arr[$p] 是 当前已知的最小值
if($arr[$p] > $arr[$j]) {
//比较，发现更小的,记录下最小值的位置；并且在下次比较时，
// 应该采用已知的最小值进行比较。
$p = $j;
}
}
//已经确定了当前的最小值的位置，保存到$p中。
//如果发现 最小值的位置与当前假设的位置$i不同，则位置互换即可
if($p != $i) {
$tmp = $arr[$p];
$arr[$p] = $arr[$i];
$arr[$i] = $tmp;
}
}
//返回最终结果
return $arr;
}3. Insertion sort method
Insertion sort method idea: Insert the elements to be sorted into the specified position of the array where the sort number has been assumed.
function insert_sort(&$arr) {
//区分 哪部分是已经排序好的
//哪部分是没有排序的
//找到其中一个需要排序的元素
//这个元素 就是从第二个元素开始，到最后一个元素都是这个需要排序的元素
//利用循环就可以标志出来
//i循环控制 每次需要插入的元素，一旦需要插入的元素控制好了，
//间接已经将数组分成了2部分，下标小于当前的（左边的），是排序好的序列
for($i=1, $len=count($arr); $i<$len; $i++) {
//获得当前需要比较的元素值。
$tmp = $arr[$i];
//内层循环控制 比较 并 插入
for($j=$i-1;$j>=0;$j--) {
//$arr[$i];//需要插入的元素; $arr[$j];//需要比较的元素
if($tmp < $arr[$j]) {
//发现插入的元素要小，交换位置
//将后边的元素与前面的元素互换
$arr[$j+1] = $arr[$j];
//将前面的数设置为 当前需要交换的数
$arr[$j] = $tmp;
} else {
//如果碰到不需要移动的元素
//由于是已经排序好是数组，则前面的就不需要再次比较了。
break;
}
}
}
//将这个元素 插入到已经排序好的序列内。
//返回
return $arr;
}4. Quick sorting method
function quick_sort(&$arr) {
//先判断是否需要继续进行
$length = count($arr);
if($length <= 1) {
return $arr;
}
//如果没有返回，说明数组内的元素个数 多于1个，需要排序
//选择一个标尺
//选择第一个元素
$base_num = $arr[0];
//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
//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; $i++) {
if($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);
}Related recommendations:
##phpBasic Algorithm_PHP Tutorial
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