**Tree Data Structure-**

Before you go through this article, make sure that you have gone through the previous article on **Tree Data Structure**.

We have discussed-

- Tree is a non-linear data structure.
- In a tree data structure, a node can have any number of child nodes.

In this article, we will discuss about Binary Trees.

**Binary Tree-**

Binary tree is a special tree data structure in which each node can have at most 2 children. Thus, in a binary tree, Each node has either 0 child or 1 child or 2 children. |

**Example-**

__Unlabeled__** Binary Tree-**

__Unlabeled__

A binary tree is unlabeled if its nodes are not assigned any label. |

**Example-**

Consider we want to draw all the binary trees possible with 3 unlabeled nodes.

Using the above formula, we have-

Number of binary trees possible with 3 unlabeled nodes

= ^{2 x 3}C_{3} / (3 + 1)

= ^{6}C_{3} / 4

= 5

Thus,

- With 3 unlabeled nodes, 5 unlabeled binary trees are possible.
- These unlabeled binary trees are as follows-

__Labeled__** Binary Tree-**

__Labeled__

A binary tree is labeled if all its nodes are assigned a label. |

**Example-**

Consider we want to draw all the binary trees possible with 3 labeled nodes.

Using the above formula, we have-

Number of binary trees possible with 3 labeled nodes

= { ^{2 x 3}C_{3} / (3 + 1) } x 3!

= { ^{6}C_{3} / 4 } x 6

= 5 x 6

= 30

Thus,

- With 3 labeled nodes, 30 labeled binary trees are possible.
- Each unlabeled structure gives rise to 3! = 6 different labeled structures.

Similarly,

- Every other unlabeled structure gives rise to 6 different labeled structures.
- Thus, in total 30 different labeled binary trees are possible.

**Types of Binary Trees-**

Binary trees can be of the following types-

- Rooted Binary Tree
- Full / Strictly Binary Tree
- Complete / Perfect Binary Tree
- Almost Complete Binary Tree
- Skewed Binary Tree

**1. Rooted Binary Tree-**

A **rooted binary tree** is a binary tree that satisfies the following 2 properties-

- It has a root node.
- Each node has at most 2 children.

**Example-**

**2. Full / Strictly Binary Tree-**

- A binary tree in which every node has either 0 or 2 children is called as a
**Full binary tree**. - Full binary tree is also called as
**Strictly binary tree**.

**Example-**

Here,

- First binary tree is not a full binary tree.
- This is because node C has only 1 child.

**3. Complete / Perfect Binary Tree-**

A **complete binary tree** is a binary tree that satisfies the following 2 properties-

- Every internal node has exactly 2 children.
- All the leaf nodes are at the same level.

Complete binary tree is also called as **Perfect binary tree**.

**Example-**

Here,

- First binary tree is not a complete binary tree.
- This is because all the leaf nodes are not at the same level.

**4. Almost Complete Binary Tree-**

An **almost complete binary tree** is a binary tree that satisfies the following 2 properties-

- All the levels are completely filled except possibly the last level.
- The last level must be strictly filled from left to right.

**Example-**

Here,

- First binary tree is not an almost complete binary tree.
- This is because the last level is not filled from left to right.

**5. Skewed Binary Tree-**

A **skewed binary tree** is a binary tree that satisfies the following 2 properties-

- All the nodes except one node has one and only one child.
- The remaining node has no child.

**OR**

A **skewed binary tree** is a binary tree of n nodes such that its depth is (n-1).

**Example-**

To gain better understanding about Binary Tree and its types-

**Also Read-****Binary Tree Traversal**

**Download Handwritten Notes Here-**

**Next Article-****Binary Tree Properties**

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