# What Is Complete Binary Tree in Data Structure?

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Angela Bailey

A complete binary tree is a type of binary tree in which all levels of the tree are completely filled except possibly for the last level, which is filled from left to right. This means that all nodes at each level, except possibly the last level, have two children. In other words, a complete binary tree is a binary tree in which all nodes have either 0 or 2 children.

## Properties of a Complete Binary Tree

A complete binary tree has some interesting properties:

• Property 1: In a complete binary tree with n levels, the number of nodes is between 2n-1 and 2n-1.
• Property 2: The height of a complete binary tree with n nodes is O(log2(n)).
• Property 3: The maximum number of nodes at the last level of a complete binary tree occurs when all preceding levels are completely filled. In this case, the number of nodes at the last level is equal to half the number of nodes in the tree.
• Property 4: A complete binary tree can be efficiently represented using an array where each element represents a node and its indices follow a specific pattern.

## Distinguishing Complete Binary Trees from Other Types

A complete binary tree differs from other types of binary trees such as full binary trees and perfect binary trees. While both full and perfect binary trees have all levels completely filled, they differ in terms of node positions.

• In a full binary tree, every node has either 0 or 2 children, and all leaf nodes are at the same level.
• In a perfect binary tree, all nodes have 2 children and all leaf nodes are at the same level. It is a special case of a complete binary tree.

## Applications of Complete Binary Trees

Complete binary trees have several applications in computer science and data structures:

• Heap data structure: Complete binary trees are used to implement heaps, which are widely used in priority queues and sorting algorithms.
• Huffman coding: Complete binary trees are used in Huffman coding, an algorithm for lossless data compression.
• Binary search trees: Although complete binary trees do not necessarily satisfy the properties of binary search trees, they can be used as an efficient representation for sorted arrays. Each element in the array corresponds to a node in the complete binary tree.

### In Conclusion

A complete binary tree is a special type of binary tree where all levels, except possibly the last one, have two children for each node. It has various properties that make it useful in different applications. Understanding complete binary trees is essential for mastering data structures and algorithms.