[Can two numbers become same] Determine if it is possible to make S equal to T #numbertheory

can_reach.py

## Select an element x in S, and remove one occurrence of x in S. 
## Then, either insert x+k into S, or insert |x−k| into S. 
## Determine if it is possible to make S equal to T.
def can_reach(a, b, k):
    """
    k = 5
    2 9 6
    8 4 11
    Can you reach 8 from 2 by repeatedly adding/subtracting k?
    Yes: 2-5 = -3; -3 - 5 = -8; abs(-8) = 8
    """
    if k == 0:
        return abs(a) == b
    return (b - a) % k == 0 or (-b - a) % k == 0