$1.$ Implement the Euclidean Algorithm. $(15$ points$)$

Given two integer inputs a and b$,$ return the greatest common divisor $($gcd$).$

o You MUST show the following tests $($You can change the function name$).$

a$)$ gcd$(0,15)$

b$)$ gcd$(39,13)$

c$)$ gcd$(31356,55576)$