Given meeting times, find the minimum number of conference rooms required.
Here's different from activity selection. You are not selecting meetings; you must attend all of them. The question is: how many rooms do you need?
The answer equals the maximum number of overlapping meetings at any time. Think of it as: how many meetings happen simultaneously at the busiest moment? You need enough rooms to handle the peak overlap. The problem asks for the maximum concurrent meetings, not the maximum non-overlapping.