Test if a range intersects another range of numbers

Question

I have 2 range of numbers:

• $startTime to $endTime
• $offerStartTime to $offerEndTime

Answer 1

If you are just checking whether any part of the offer overlaps any part of the range, it's simple.

if ($offerStartTime < $endTime && $offerEndTime > $startTime)  {
    echo 'The ranges overlap';
}

Here's a picture representing all the possibilities of overlap and non-overlap to visualize why this works.

Based on your inputs and expected false outputs, I used < and >. If you wanted to also include ranges that intersected at a point, you would need to use <= and >= instead.