# Frogs Collision

Simple

A frog hopping along on the infinite two-dimensional grid of integers is represented as a 4-tuple of the form `(x, y, dx, dy)` so that `x, y` is the frogâ€™s starting position at time `t = 0`, and `dx, dy` is its constant direction vector for each hop. Time advances in discrete integer steps so that each frog makes one hop at every tick of the clock.

Given two frogs `frog1, frog2`, that initially stand on different squares, return the time when both frogs hop into the same square. If these two frogs never hop into the same square at the same time, this function should return `None`.

Let's look at the example `(0, 0, 0, 2), (0, 10, 0, 1)`. `X`'s are equal and don't change (`dx1 == dx2 == 0`), so we may ignore them.

Your function should not contain any loops whatsoever, but the result should be computed with conditional...

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