$9\mathrm{.}4\mathrm{.}4$: Complete the code to swap elements in an array.

$597714\mathrm{.}2988516.$qx$3$zqy$7$

Complete this code to swap the first and last element of the given array. Do nothing if the array is empty.

$597714\mathrm{.}2988516.$qx$3$zqy$7$

Compute the distance between the positions of the first and last zero element in the given array. For example, if the array is

$301049506$ your algorithm should yield $7-1=6.$

If the array contains a single zero, return $0.$ If it doesn't contain any zeroes, return a negative value.