Either the first range contains the second, or the second range contains the first. The first case looks something like:
----x0------y0-----
--x1-----------y1--
So, we can check that x1 <= x0 and y0 <= y1. The other case is similar, just with the variables flipped around.
An easy way to check for overlap is by comparing the larger start position and the smaller ending position.
If max(x0, x1) <= min(y0, y1), then we have overlap:
----x0-------y0------
--------x1-------y1--
Nothing too complicated today, the overlap check for part 2 is a nice-to-know trick.