Question

我有两个用户定义排序函数的实现：堆排序和快速排序。我一直在权衡各种排序方法的好处/缺点，并决定做一些基准测试。

为什么PHP的原生usort()功能如此之快？

我知道Heap Sort是O（log，n）并且它有它的好处，我也理解为什么快速排序在这个实现中优于heapsort;但为什么usort()占主导地位呢？ 可能是因为usort是php（源代码）的一部分，它的内部工作是利用C源代码吗？

以下是我的结果和实现：HeapSort.php，QuickSort.php和入口点sort.php

输出

Heapsort: 11.894743
Quicksort: 5.641383
usort: 1.180634
---------------------------------------
Total Time: 18.716766

sort.php

<?php
/* Author Jacob Psimos */
define('SIZE', 200000);

include('HeapSort.php');
include('QuickSort.php');

$array = array();
$array2 = array();
$array3 = array();
for($i = 0; $i < SIZE; $i++){
    array_push($array, array('value' => SIZE - $i));
    array_push($array2, array('value' => SIZE - $i));
    array_push($array3, array('value' => SIZE - $i));
}

$start1 = microtime(true);
array_heapsort($array, 'cmp', SIZE);
$end1 = microtime(true);
//unset($array);

$start2 = microtime(TRUE);
array_quicksort($array2, 0, SIZE - 1, 'cmp');
$end2 = microtime(TRUE);
//unset($array2);

$start3 = microtime(TRUE);
usort($array3, 'cmp');
$end3 = microtime(TRUE);
//unset($array3);

printf("Heapsort: %f\n", $end1 -  $start1);
printf("Quicksort: %f\n", $end2 - $start2);
printf("usort: %f\n", $end3 - $start3);
echo "---------------------------------------\n";
printf("Total Time: %f\n", $end3 - $start1);

function cmp($a, $b){
    if($a['value'] > $b['value']){
        return 1;
    }else if($a['value'] < $b['value']){
        return -1;
    }else{
        return 0;
    }
}
?>

HeapSort.php

<?php
/* Author Jacob Psimos */
function array_heapsort(&$array, $cmp_function, $total){
    $total--;
    for($i = (integer)($total / 2); $i >= 0; $i--){
        _heapify_array($array, $i, $total, $cmp_function);
    }

    for($i = $total; $i > 0; $i--){
        _array_swap($array, 0, $i);
        $total--; 
        _heapify_array($array, 0, $total, $cmp_function);   
    }

}

function _array_swap(&$array, $a, $b){
    $temp = $array[$a];
    $array[$a] = $array[$b];
    $array[$b] = $temp;
}

function _heapify_array(&$array, $i, $total, $cmp_function){
    $left = $i * 2;
    $right = $left + 1;
    $grt = $i;

    if($left <= $total){
        $direction = call_user_func($cmp_function, $array[$left], $array[$grt]);
        if($direction >= 0){
            $grt = $left;   
        }
    }

    if($right <= $total){
        $direction = call_user_func($cmp_function, $array[$right], $array[$grt]);
        if($direction >= 0){
            $grt = $right;  
        }
    }

    if($grt != $i){
        _array_swap($array, $i, $grt);
        _heapify_array($array, $grt, $total, $cmp_function);
    }
}
?>

QuickSort.php

<?php
/* Source: Google search for 'PHP quicksort', I could not find an author
all I could find was 'Powered by hackerrank.com' -jp */
function array_quicksort(&$array, $left, $right, $cmp_function){
    $i = _array_partition($array, $left, $right, $cmp_function);

    if($left < $i - 1){
        array_quicksort($array, $left, $i - 1, $cmp_function);
    }

    if($right > $i){
        array_quicksort($array, $i, $right, $cmp_function);
    }
}

function _array_partition(&$array, $left, $right, $cmp_function){
    $pivot = $array[(integer)($left + $right) / 2];

    while($left <= $right){
        while(call_user_func($cmp_function, $array[$left], $pivot) < 0){
            $left++;
        }

        while(call_user_func($cmp_function, $array[$right], $pivot) > 0){
            $right--;
        }

        if($left <= $right){
            _array_swap($array, $left, $right);
            $left++;
            $right--;
        }
    }
    return $left;
}
?>

PHP：排序函数基准测试的比较

0 个答案: