# Binary Tree Introduction!

A binary tree is a tree data structure in which each node has at most two children, which are referred to as the left child and the right child. A binary tree can be visualized as having a hierarchical structure, with each node representing a "parent" and its children representing "descendants." The topmost node in a binary tree is called the root, and the nodes that have no children are called leaf nodes.

Binary trees are used in various algorithms, such as in tree traversals, searching and sorting algorithms. They also have many applications, including in file systems and database indexing.

In addition, there are various types of binary trees, such as binary search tree, AVL tree, splay tree, and many more. Each type of binary tree has its own unique characteristics and uses.

## How Does Binary Tree Work?

A binary tree works by recursively dividing the tree into two subtrees, a left subtree and a right subtree, until each subtree contains only a single element. Each node in a binary tree has at most two child nodes, a left child and a right child.

The root node is the topmost node in the tree and serves as the starting point for traversing the tree. The left and right subtrees of the root are each themselves binary trees, and can be traversed recursively.

The recursive nature of binary trees allows for efficient insertion, deletion, and searching operations. For example, when searching for a specific value in a binary search tree, the algorithm can eliminate half of the remaining elements in the tree with each comparison, making the search time efficient.

It also allows for various types of traversals like pre-order, in-order, post-order and level-order. Each traversal visits the nodes in a different sequence, and each has its own use case.

In addition, due to its efficient search and memory usage, binary trees are used in many algorithms such as self-balancing trees, decision trees, Huffman coding and many more.

## Examples of Binary Tree

``````class Node:
def __init__(self, data):
self.left = None
self.right = None
self.data = data

class BinaryTree:
def __init__(self):
self.root = None

def insert(self, data):
new_node = Node(data)
if self.root is None:
self.root = new_node
else:
current = self.root
while True:
if data < current.data:
if current.left is None:
current.left = new_node
break
else:
current = current.left
elif data > current.data:
if current.right is None:
current.right = new_node
break
else:
current = current.right

def search(self, data):
current = self.root
while current is not None:
if data == current.data:
return True
elif data < current.data:
current = current.left
else:
current = current.right
return False

def inorder_traversal(self, node):
if node is not None:
self.inorder_traversal(node.left)
print(node.data)
self.inorder_traversal(node.right)

def preorder_traversal(self, node):
if node is not None:
print(node.data)
self.preorder_traversal(node.left)
self.preorder_traversal(node.right)

def postorder_traversal(self, node):
if node is not None:
self.postorder_traversal(node.left)
self.postorder_traversal(node.right)
print(node.data)

tree = BinaryTree()
tree.insert(5)
tree.insert(3)
tree.insert(7)
tree.insert(1)
tree.insert(4)
tree.insert(6)
tree.insert(8)

print("Inorder traversal:")
tree.inorder_traversal(tree.root)

print("Preorder traversal:")
tree.preorder_traversal(tree.root)

print("Postorder traversal:")
tree.postorder_traversal(tree.root)

print(tree.search(4))
print(tree.search(9))``````

## Types of Binary Tree

There are several types of binary trees, some of the most common include:

1. Full Binary Tree: A binary tree in which every node has either 0 or 2 children.

2. Complete Binary Tree: A binary tree in which every level is completely filled except possibly the last level and the last level has all keys as left as possible.

3. Perfect Binary Tree: A binary tree in which all internal nodes have two children and all leaves have the same depth or same level.

4. Balanced Binary Tree: A binary tree in which the height of the left and right subtrees of every node differ by at most 1. Examples of balanced binary trees include AVL Trees and Red-black Trees.

5. Skewed Binary Tree: A binary tree in which the left or right subtrees of every node differ in height by more than 1. Examples of skewed binary trees include Left Skewed Tree or Right Skewed Tree.

6. Degenerate (or pathological) tree: A tree in which every internal node has one child.

7. Extended Binary Tree: A binary tree in which each node has three pointers, left, right, and nextSibling pointers.

8. Binary Search Tree (BST): A type of binary tree where the value of each node is greater than or equal to the values in its left subtree and less than or equal to the values in its right subtree.

Each type of binary tree has its own specific use cases and advantages. For example, a balanced binary tree such as AVL tree allows for efficient insertion and deletion, while a binary search tree allows for efficient searching.

## Applications of Binary Tree

Binary trees have many applications in computer science and software engineering. Some of the most common applications include:

1. Data Storage: Binary trees are often used to store data in a hierarchical structure. For example, a file system on a computer uses a hierarchical directory structure that can be represented by a binary tree.

2. Searching and Sorting: Binary search trees (BSTs) are used to efficiently search for a specific value in a large set of data. The structure of a BST allows for an efficient search by repeatedly dividing the search interval in half.

3. Symbol Tables: Symbol tables are used to store a mapping of keys to values. They are used in a variety of programming languages and in compilers to store information about variables and functions. Many symbol tables are implemented using binary search trees.

4. Expression Trees: Expression trees are used to represent mathematical expressions in a tree-like structure. The leaves of the tree represent the operands, while the internal nodes represent the operators.

5. Graphs: Graphs can be represented using an adjacency list or an adjacency matrix. Both of these representations can be implemented using binary trees.

6. Huffman Coding: Huffman coding is a compression algorithm that is used to compress data by representing frequently occurring symbols with shorter bit sequences. Huffman trees are used to generate the encoding for each symbol in the data.

7. Priority Queues: Priority queues are data structures that store a collection of elements with associated priorities. The priority queue allows for efficient retrieval of the element with the highest priority (or lowest, depending on how the priority queue is implemented). Some priority queue implementations, such as heaps, use a binary tree-like structure to efficiently maintain the priority order of the elements.

8. Decision Making: Decision trees are a popular tool in decision making and machine learning. It is a tree where each internal node represents a test on an attribute, each branch represents an outcome of the test, and each leaf node represents a class label (decision taken after computing all attributes).

9. Game AI: In games such as chess, the game state can be represented by a binary tree where each node represents a possible move or game state. The tree can be used to analyze possible moves and determine the best move for the computer to make.

10. Parsing: In compilers, parsing is the process of analyzing a string of symbols, either in natural language or computer languages, according to the rules of a formal grammar. Some parsing algorithms, such as Earley parser and CYK parser, use binary trees to represent the parsed input.

## Time and Space Complexity of Binary Tree

The time and space complexity of binary tree operations depends on the specific implementation and the type of binary tree.

• Insertion: In a balanced binary tree, insertion has an average time complexity of O(log n) and a worst-case time complexity of O(n) in the case of a degenerate tree. In the case of a binary search tree, the average time complexity of insertion is O(log n) and the worst-case time complexity is O(n) if the tree becomes skewed.
• Searching: In a balanced binary tree, searching has an average time complexity of O(log n) and a worst-case time complexity of O(n) in the case of a degenerate tree. In the case of a binary search tree, the average time complexity of searching is O(log n) and the worst-case time complexity is O(n) if the tree becomes skewed.
• Deletion: In a balanced binary tree, deletion has an average time complexity of O(log n) and a worst-case time complexity of O(n) in the case of a degenerate tree. In the case of a binary search tree, the average time complexity of deletion is O(log n) and the worst-case time complexity is O(n) if the tree becomes skewed.
• Traversal: In a binary tree, traversal (inorder, preorder, postorder) has a time complexity of O(n) where n is the number of nodes in the tree.
• Space: The space complexity of a binary tree is O(n) where n is the number of nodes in the tree.

It is important to note that these complexities are for worst case scenario and in practice the actual time and space complexity of a specific implementation may be better or worse than the worst case scenarios.

### Advantages of binary trees include

1. Efficient search: Binary search trees (BSTs) allow for efficient search operations with an average time complexity of O(log n)

2. Flexibility: Binary trees can be used to implement a wide variety of data structures, such as symbol tables, priority queues, and decision trees.

3. Easy to implement: Binary trees are relatively easy to implement, especially compared to other data structures such as graphs and linked lists.

4. Space efficient: Binary trees can be used to represent large amounts of data in a relatively small amount of memory.

### Disadvantages of binary trees include

1. Complexity: Some operations on binary trees can be complex and difficult to implement, such as balancing a tree and deleting a node in a balanced binary tree.

2. Unbalanced: If a binary tree becomes unbalanced, the performance of search, insertion, and deletion operations can degrade to O(n).

3. Time consuming: Some operations, such as traversals, can be time-consuming, with a time complexity of O(n).

4. Not suitable for all situations: Some types of data or use cases are not well-suited to binary trees, and other data structures may be more appropriate.

It's important to note that these are general pros and cons of binary trees and the specific advantages and disadvantages may vary depending on the type of binary tree and the specific use case.