PHP implements four basic sorting algorithms_PHP tutorial

php implements four basic sorting algorithms

Sorted array: $arr(1,43,54,62,21,66,32,78,36,76,39);

Sort using four sorting algorithms

Bubble sorting: (Idea: Compare and adjust the unsorted numbers from front to back at the same time, with large ones sinking and small ones rising)

    $arr=array(1,43,54,62,21,66,32,78,36,76,39);   
    function bubbleSort($arr)  
    {   
    $len=count($arr);  
    //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;  
    }  

Selection sort: (Find the smallest number in a set of numbers and exchange it with the first number, and then find the smallest number among the remaining numbers and exchange it with the number in the second position,

Continue one at a time until the penultimate number is compared with the last number)

    function selectSort($arr) {  
    //双重循环完成，外层控制轮数，内层控制比较次数  
    $len=count($arr);  
    for($i=0; $i<$len-1; $i++) {  
    //先假设最小的值的位置  
    $p = $i;  
      
    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;  
    }  

Insertion sort: (Assuming that the previous numbers are already in order, now we need to insert the n-th number into the previous ordered numbers so that these n numbers are also in order.

Repeat this cycle until everything is in order)

    function insertSort($arr) {  
    $len=count($arr);   
    for($i=1, $i<$len; $i++) {  
    $tmp = $arr[$i];  
    //内层循环控制，比较并插入  
    for($j=$i-1;$j>=0;$j--) {  
    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];  
    $arr[$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;  
    }  
    }  
    }  
    return $arr;  
    }  

Quick sort: (Select a reference element, usually the first element or the last element. Divide the column to be sorted into two parts through one scan,

Part of it is smaller than the base element, and part of it is greater than or equal to the base element. At this time, the base element is at its correct position after sorting, and then the same method is used to recursively

Sorting divided into two parts. )

function quickSort($arr) {  
//先判断是否需要继续进行  
$length = count($arr);  
if($length <= 1) {  
return $arr;  
}  
//选择第一个元素作为基准  
$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(); //小于基准的  
$right_array = array(); //大于基准的  
for($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  
$left_array = quick_sort($left_array);  
$right_array = quick_sort($right_array);  
//合并  
return array_merge($left_array, array($base_num), $right_array);  
}  

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