Here's what you learned in this section:
Maps store key-value pairs with fast lookups using hash tables
Create maps with make() or literals. Nil maps panic on write
The comma-ok idiom checks if a key exists
delete() removes entries. Deleting missing keys is safe
Map iteration order is random. Sort keys for ordered output
Keys must be comparable. Slices and maps cannot be keys
Maps are reference types. Functions can modify them directly
Use map[T]bool or map[T]struct{} to implement sets