Let n = number of times each kangaroo hops to eventually land at the same exact distance. To see whether that does happen we need the following expression to be true:

x1 + (v1 * n) = x2 + (v2 * n)

We can check this by looking at the sample input 0, 3, 5, 2 for x1, v1, x2, v2 respectively.

0 + 3n = 5 + 2n n = 5

This means it takes the kangaroos jumping 5 times to land at the same distance:

0 > 3 > 6 > 9 > 12 > 15

5 > 7 > 9 > 11 > 13 > 15

Now that we know the equation is right, let's move n to one side:

(v1 * n) - (v2 * n) = x2 - x1

n(v1 - v2) = x2 - x1

n = (x2 - x1) / (v1 - v2)

We don't know what the value of n will be, but we know that it must be an integer. If the division solves for a whole integer, we know there is no remainder value. So, we use modular division

(x2 - x1) % (v1 - v2) == 0 (meaning no remainder value, and therefore the division solves for an integer)