Randomly remove several different numbers from an array

/*
 * 此程序是从一个不重复的数组中随机的取出若干个不同的元素
 * 难点是防止在取数的时候出现已经取到过的情况（特别是取到最后），需要尽可能的降低碰撞
 */
//第一种算法，CSDN上别人的想法
/*
$num = 0;
$array = array(1, 2, 3, 4, 5, 6, 7, 8, 9);
$arr = array();
$g = 5;
$tag = true;
while ($tag) {
    $count = count($array);
    $t = rand(0, 1);
    if ($t == 1) {
        $arr[] = $array[$num];
        unset($array[$num]);
    }
    $num ++;
    if (count($arr) == $g) {
        $tag = false;
    }
    if ($num == $count) {
        $num = 0;   //循环
    }
}


var_dump($arr);
*/
//第二种算法，自己想的。
//可以在每次取出数据之后将该数据和最后没有获取的数据替换，然后再去没有取得的数据中随机获取值


function swap(&$a, &$b)
{
    $temp = $b;
    $b = $a;
    $a = $temp;
}


$result = array();
$src = array();
for($i = 0 ; $i < 40 ; $i++)
{
    $src[] = $i + 1;
}
$arr_len = count($src);
$count = 20;
$index = 0;
while($index < $count)
{
    $random = rand(0, $arr_len - $index - 1);
    $result[] = $src[$random];
    swap($src[$random] , $src[$arr_len - $index - 1]);
    $index += 1;
}


print_r(json_encode($result));
print_r(json_encode($src));

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