The number goes on the other end of the line

transcript

A hotel room holds up to four guests. And every guest is in exactly one room. You write four beside Room. That is wrong.

The rule is simple. A number counts the class it sits beside, not the one it leaves. Read it as: how many of this, for one of the other.

Beside Guest goes zero to four. One room holds that many guests. Beside Room goes one. Each guest is in exactly one room.

Now swap them. Zero to four beside Room says a guest can be in four rooms. And one beside Guest says a room holds exactly one guest. Different design. Same line, same boxes, two different claims. That is why the end matters.

And every number becomes a check in the code. Zero to four guests is a limit that check-in enforces. When you draw a number, say the check out loud.

The number counts the class beside it. Always.

Full breakdown in the lecture.