Back to Resources

Trees

by Eddie Huang

Some Notation

Nodes in a tree can have a parent and/or children
The top node is called the root. Nodes with no children are leaves. All other nodes are internal. The height of a tree is one less than the number of levels. For example, an empty tree has height -1 and a tree with just the root has height 0
This is a 4-ary tree. An n-ary has a maximum of n children among all of its nodes. In this course, we mainly study 2-ary (binary) trees, which are trees with at most 2 children per node

Traversals

Since nodes in a tree can have multiple children, there are multiple ways of traversing trees. Here we discuss three main traversals:

Preorder, Inorder, and Postorder traversals of a tree

Types of Trees

Perfect
Every level is completely filled
Complete
Every level except for the last is completely filled, and in the last level all the nodes are pushed to the left as much as possible
Full
Every node either has no children or the maximum number of children possible