The Design Patterns That Come Up in This Round

A design pattern is a named solution to a problem that keeps happening. There are dozens of them. Six appear in this round often enough to be worth knowing by name.

Knowing the name is worth something. It turns a paragraph of explanation into two words. It also tells the interviewer you have seen the problem before. Using one where it does not belong costs more than not knowing it. So each pattern below comes with the signal that says it applies.

Strategy

The signal: one operation has several interchangeable versions, and the right one is chosen at run time.