统计总和：线性递归、线性迭代、算法计算(耗时比较)

统计总和的几种方法比较
//1：线性递归
function sumRecursion(int $n): int{
    if($n < 1){
        return 0;
    }
    return sumRecursion($n-1) + $n-1;
}
//2：线性迭代
function sumFor(int $n): int{
    $sum = 0;
    for($i=1;$i<=$n;$i++){
        $sum+=$i;
    }
    return $sum;
}
//3：算法
function sum(int $n): int{
    return ($n+1) * $n / 2;
}

//方法一直接报错
$number = 10000000;
$t1 = microtime(true);
$res = sumRecursion($number);
$t2 = microtime(true);
echo '耗时'.round($t2-$t1,3).'秒';
var_dump($res);

Fatal error: Uncaught Error: Maximum function nesting level of '256' reached, aborting!

//方法二耗时四秒多
$number = 10000000;
$t1 = microtime(true);
$res = sumFor($number);
$t2 = microtime(true);
echo '耗时'.round($t2-$t1,3).'秒';
var_dump($res);

耗时4.335秒 G:\study\sum.php:27:int 50000005000000

//使用算法，答案秒出
$number = 10000000;
$t1 = microtime(true);
$res = sum($number);
$t2 = microtime(true);
echo '耗时'.round($t2-$t1,3).'秒';
var_dump($res);

耗时0秒 G:\study\sum.php:27:int 50000005000000