Introduction to bubbling, binary insertion, and quick sort algorithms

1. Bubble sorting algorithm
Process:
1. Traverse the entire array and compare every pair of adjacent elements, such as $ a[$i]>$a[$i 1] swaps positions, and each comparison eliminates a reverse order.
2. After each cycle, the number of times it needs to be cycled next time is reduced by 1.

<?php
// 冒泡排序
$arr = createarr(20);
printarr($arr);
popsort($arr);
printarr($arr);
function createarr($num=10){
    $arr = array();
    for($i=0; $i<$num; $i++){
        array_push($arr, mt_rand(0,999));
    }
    return $arr;
}
function printarr($arr){
    echo &#39;arr:&#39;.implode(&#39;,&#39;, $arr).&#39;<br>&#39;;
}
function popsort(&$arr){
    for($i=0,$length=count($arr)-1; $i<$length; $i++){
        for($j=0; $j<$length-$i; $j++){
            if($arr[$j]>$arr[$j+1]){
                $tmp = $arr[$j];
                $arr[$j] = $arr[$j+1];
                $arr[$j+1] = $tmp;
            }
        }
    }    
}
?>

2. Dichotomous insertion sort

Process:
1. First of all, the original array is an ordered sequence, $low=0 $high=count($arr)-1.
2. Compare the number to be inserted with the element in the middle of the array.
If it is larger than the middle element, $low=$mid 1 will be used as the beginning of the array for the next judgment.
If it is smaller than the middle element, $high=$mid-1 will be used as the end of the array for the next judgment.
3. Until $low>$high ends, $low is the position where the new element is inserted.
4. Move all elements starting from $low in the array backward by one, and then insert new elements at the $low position.

<?php
// 二分法插入排序
$arr = createarr(20);
$key = mt_rand(0,99);
printarr($arr);
echo &#39;key=&#39;.$key.&#39;<br>&#39;;
binsort($arr, $key);
printarr($arr);
function createarr($num=10){
    $arr = array();
    for($i=0; $i<$num; $i++){
        array_push($arr, mt_rand(0,99));
    }
    sort($arr); // 有序序列
    return $arr;
}
function printarr($arr){
    echo &#39;arr:&#39;.implode(&#39;,&#39;, $arr).&#39;<br>&#39;;
}
function binsort(&$arr, $key){
    $low = 0;
    $high = count($arr)-1;
    while($low<=$high){
        $m = $low + (int)(($high-$low)/2);
        $mkey = $arr[$m];
        if($key>=$mkey){
            $low = $m + 1;
        }else{
            $high = $m - 1;
        }
    }
    // 移动插入位置之后的元素,插入新元素
    for($i=count($arr)-1; $i>=$low; $i--){
        $arr[$i+1] = $arr[$i];
    }
    $arr[$low] = $key;
}
?>

3. Quick sort
Process:
1. Find an element in the array as the key, usually The first element of the array is used as the key
2. i=0, j=array length-1
3. j-- When arr[j]4. i When arr[i]>key, arr[i] and arr[j] exchange positions
5. Repeat 3,4 until i==j, complete.
6. Execute 1, 2, 3, 4, 5 (recursively) for the left and right sets of elements separated by key.

<?php
// 快速排序
$arr = createarr(20);
printarr($arr);
quicksort($arr, 0, count($arr)-1);
printarr($arr);
function createarr($num=10){
    $arr = array();
    for($i=0; $i<$num; $i++){
        array_push($arr, mt_rand(0,999));
    }
    return $arr;
}
function printarr($arr){
    echo &#39;arr:&#39;.implode(&#39;,&#39;, $arr).&#39;<br>&#39;;
}
function quicksort(&$arr, $low, $high){
    if($low>=$high){
        return ;
    }
    $key = $arr[$low];
    $i = $low;
    $j = $high;
    $flag = 1;
    while($i!=$j){
        switch($flag){
            case 0:
                if($arr[$i]>$key){
                    $tmp = $arr[$i];
                    $arr[$i] = $arr[$j];
                    $arr[$j] = $tmp;
                    $flag = 1;
                }else{
                    $i++;
                }
                break;
            case 1:
                if($arr[$j]<$key){
                    $tmp = $arr[$i];
                    $arr[$i] = $arr[$j];
                    $arr[$j] = $tmp;
                    $flag = 0;
                }else{
                    $j--;
                }
                break;
        }
    }
    quicksort($arr, $low, $i-1);
    quicksort($arr, $i+1, $high);
}
?>

This article explains bubbling, dichotomous insertion, and quick sorting algorithms. For more related content, please pay attention to the PHP Chinese website.

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