A binary tree is a finite set of elements that is either empty or is partitioned into three disjoint subsets. The first subset contains a single element called the root of the tree.

The other two subset are themselves binary trees, called the left and right sub trees of the original tree.

A left or right sub tree can be empty. Each element of a binary tree is called a node of the tree.

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The other two subset are themselves binary trees, called the left and right sub trees of the original tree.

A left or right sub tree can be empty. Each element of a binary tree is called a node of the tree.

In computer science, 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[1].

binary tree |

According to above figure, all the elements 8, 4, 12 ,2, 5, 9, 14 etc are called as node and here 8 is the root node. Which is simply known as the parent of 4 and 12 and grand parent of 2, 5 and 9, 14. The 4 is the left sub-tree and 12 is the right sub tree.

## Types of Binary Trees

- Strictly Binary Tree
- Complete Binary Tree
- Almost Complete Binary Tree

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*Strictly Binary Tree*

*Strictly Binary Tree*

**If every nonleaf node in a binary tree has nonempty left and right sub-trees, the tree is termed as a strictly binary tree.**

If every non-leaf node in a binary tree has nonempty left and right subtrees, the tree is termed a strictly binary tree. Or, to put it another way, all of the nodes in a strictly binary tree are of degree zero or two, never degree one.[2]

### Complete Binary Tree

A complete binary tree of depth d is the strictly binary tree all of whose leaves are at level d. In a complete binary tree, there is exactly one node at level 0, two nodes at level 1, four nodes at level 2 and so on.

### Almost Complete Binary Tree

A binary tree of depth d is an almost complete binary tree, if

- Any node nd at level less than d-1 has two sons.
- For any node nd in the tree with a right descendant at level d, nd must have a left son and every left descendant of nd is either a leaf at level dd or has two sons.
- The nodes of an almost complete binary tree are numbered in a way that the root is assigned the number 1, a left son is assigned twice the number assigned to its father, and a right son is assigned one more than twice the number assigned to its father.