The three man team would work much the same way, with one hugging the right wall, a second following the left (doesn't matter which order) and the third splitting the room down the middle. The third man covers the entire room and is backup for either member to right or left. It's still the same theory as what tire iron described, but putting a third more offensive force into the room to deal with threat. We were taught that three could still get into the room and move effectively without getting shot - supposedly the reaction time of badguys isn't quick enough if they aren't ready for you. If they are waiting, someone's getting shot - that's why you take more with you. Better chance of overwhelming the shooter with several rapidly moving targets going in different directions and shooting back.
It all hinges on if the good guys have surprise. Thankfully I haven't seen it in action yet.
Add a fourth guy for rear security and you've got the dynamic entry team being taught across the courty for active shooter scenarios.