斐波那契数列实现的2种方法

// 递归法: 斐波那契数列
function fab1($n)
{
    if ($n <= 0) {
        return 0;
    }
    if ($n == 0 || $n == 1) {
        return $n;
    }
    return fab1($n - 1) + fab1($n - 2);
}

// 优化
function fab($n)
{
    $first = 0;
    $second = 1;
    $next_value = 0;
    for ($i = 2; $i <= $n; $i++) {
        $next_value = $first + $second;
        $first = $second;
        $second = $next_value;
    }
    return $next_value;
}