s, where each pair has a key and a value associated with the key ??? ??? ??? base case a simple case that can be solved easily, without recursion ??? ??? ??? Binary Tree a tree in which each node has at most two children ??? ??? ??? Boxed Number a number that is defined as an object, so that it has a runtime type and methods that can be used, e.g. Integer in Java ??? ??? ??? circularly linked list