Practical example of Complete Binary Tree is Binary Heap.
Perfect Binary Tree A Binary tree is Perfect Binary Tree in which all internal nodes have two children and all leaves are at same level.
Following are examples of Perfect Binaryr Trees.
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A Perfect Binary Tree of height h (where height is number of nodes on path from root to leaf) has 2h – 1 node.
Example of Perfect binary tree is ancestors in family. Keep a person at root, parents as children, parents of parents as their children.
Balanced Binary Tree
A binary tree is balanced if height of the tree is O(Log n) where n is number of nodes. For Example, AVL tree maintain O(Log n) height by making sure that the difference between heights of left and right subtrees is 1. Red-Black trees maintain O(Log n) height by making sure that the number of Black nodes on every root to leaf paths are same and there are no adjacent red nodes. Balanced Binary Search trees are performance wise good as they provide O(log n) time for search, insert and delete.
A degenerate (or pathological) tree A Tree where every internal node has one child. Such trees are performance-wise same as linked list.