Calculates the greatest common divisor between two or more numbers.

Use recursion.
Use array_reduce() with the gcd function to appy to all elements in the $numbers list.
Base case is when y equals 0. In this case, return x.
Otherwise, return the gcd of y and the remainder of the division x/y.

代码实现

function gcd(...$numbers)
{
  if (count($numbers) > 2) {
    return array_reduce($numbers, 'gcd');
  }

  $r = $numbers[0] % $numbers[1];
  return $r === 0 ? abs($numbers[1]) : gcd($numbers[1], $r);
}

使用样例

gcd(8, 36); // 4
gcd(12, 8, 32); // 4