十大排序算法之选择排序（2）

2.选择排序

<?php
/**
 * 基础选择排序
 *
 */
function selectionSort($sortData)
{
    $count = count($sortData);
    $sortCount = 0;
    for ($i = $count - 1; $i > 0; $i--) {
        $max = $i;
        for ($j = 0; $j < $i; $j++) {
            $sortCount++;
            if ($sortData[$max] < $sortData[$j]) {
                $max = $j;
            }
        }
        if ($max != $i) {
            $temp = $sortData[$max];
            $sortData[$max] = $sortData[$i];
            $sortData[$i] = $temp;
        }
    }
    echo 'selectionSort Count:' . $sortCount;
    echo PHP_EOL;
    return $sortData;
}

/**
 * 优化1：每次取最大和最小的
 *
 */
function selectionSort_2($sortData)
{
    $count = count($sortData);
    $sortCount = 0;
    for ($i = $count - 1, $sortFrom = 0; $i > $sortFrom; $i--, $sortFrom++) {
        $max = $i;
        $min = $sortFrom;
        for ($j = $sortFrom; $j <= $i; $j++) {
            $sortCount++;
            if ($sortData[$max] < $sortData[$j]) {
                $max = $j;
            }
            if ($sortData[$min] > $sortData[$j]) {
                $min = $j;
            }
        }
        if ($min != $sortFrom) {
            $temp = $sortData[$min];
            $sortData[$min] = $sortData[$sortFrom];
            $sortData[$sortFrom] = $temp;
        }
       //此处是先排最小值的位置，所以得考虑最大值（arr[max]）在最小位置（left）的情况。
        if ($max == $sortFrom){
            $max = $min;
        }
        if ($max != $i) {
            $temp = $sortData[$max];
            $sortData[$max] = $sortData[$i];
            $sortData[$i] = $temp;
        }
    }
    echo 'selectionSort_2 Count:' . $sortCount;
    echo PHP_EOL;
    return $sortData;
}

$testSortData = [3, 2, 9, 234, 3432, 43, 22, 33, 21312, 123];

$sortResult = selectionSort($testSortData);
echo 'selectionSort Result:';
echo PHP_EOL;
echo (implode(',', $sortResult));
echo PHP_EOL;

$sortResult = selectionSort_2($testSortData);
echo 'selectionSort_2 Result:';
echo PHP_EOL;
echo (implode(',', $sortResult));
echo PHP_EOL;