Tree

A tree is a collection of nodes

• The collection can be empty
• (recursive definition) If not empty, a tree consists of a distinguished node r (the root), and zero or more nonempty subtrees , each of whose roots are connected by a directed edge from root

Concept

• Root and Leaf
• Child and Parent
  • Every node except the root has one parent
  • A node can have an zero or more children
  • A leaf node has no children
• Sibling
  nodes with same parent

Path

• a sequence of edges

Length of a path
Depth of a node

• length of the unique path to the root

Height of a node

• length of the longest path to a leaf

Tree height

• the height of the root
• the depth of the deepest leaf

Ancestor and descendant

• If there is a path from n1 to n2
• n1 is an ancestor of n2, n2 is a descendant of n1
• Proper ancestor and proper descendant

A perfect binary tree is the tree where a node can have 0 or 2 children and all leaves are at the same depth