Binary Tree-

Before you go through this article, make sure that you gone through the previous article on Binary Trees.

We have discussed-

• Binary tree is a special tree data structure.
• In a binary tree, each node can have at most 2 children.

In this article, we will discuss about Binary Tree Traversal.

Tree Traversal-

 Tree Traversal refers to the process of visiting each node in a tree data structure exactly once.

Various tree traversal techniques are-

Depth First Traversal-

Following three traversal techniques fall under Depth First Traversal-

1. Preorder Traversal
2. Inorder Traversal
3. Postorder Traversal

Algorithm-

1. Visit the root
2. Traverse the left sub tree i.e. call Preorder (left sub tree)
3. Traverse the right sub tree i.e. call Preorder (right sub tree)

Root  Left  Right

Example-

Consider the following example-

Preorder Traversal Shortcut

Traverse the entire tree starting from the root node keeping yourself to the left.

Applications-

• Preorder traversal is used to get prefix expression of an expression tree.
• Preorder traversal is used to create a copy of the tree.

Algorithm-

1. Traverse the left sub tree i.e. call Inorder (left sub tree)
2. Visit the root
3. Traverse the right sub tree i.e. call Inorder (right sub tree)

Left  Root  Right

Example-

Consider the following example-

Inorder Traversal Shortcut

Keep a plane mirror horizontally at the bottom of the tree and take the projection of all the nodes.

Application-

• Inorder traversal is used to get infix expression of an expression tree.

Algorithm-

1. Traverse the left sub tree i.e. call Postorder (left sub tree)
2. Traverse the right sub tree i.e. call Postorder (right sub tree)
3. Visit the root

Left  Right  Root

Example-

Consider the following example-

Postorder Traversal Shortcut

Pluck all the leftmost leaf nodes one by one.

Applications-

• Postorder traversal is used to get postfix expression of an expression tree.
• Postorder traversal is used to delete the tree.
• This is because it deletes the children first and then it deletes the parent.

• Breadth First Traversal of a tree prints all the nodes of a tree level by level.
• Breadth First Traversal is also called as Level Order Traversal.

Application-

• Level order traversal is used to print the data in the same order as stored in the array representation of a complete binary tree.

To gain better understanding about Tree Traversal,

Watch this Video Lecture

Also Read- Binary Tree Properties

Problem-01:

If the binary tree in figure is traversed in inorder, then the order in which the nodes will be visited is ____?

Solution-

The inorder traversal will be performed as-

Problem-02:

Which of the following sequences denotes the postorder traversal sequence of the tree shown in figure?

1. FEGCBDBA
2. GCBDAFE
3. GCDBFEA
4. FDEGCBA

Solution-

Perform the postorder traversal by plucking all the leftmost leaf nodes one by one.

Then,

Postorder Traversal :  G , C , D , B , F , E , A

Thus, Option (C) is correct.

Problem-03:

Let LASTPOST, LASTIN, LASTPRE denote the last vertex visited in a postorder, inorder and preorder traversal respectively of a complete binary tree. Which of the following is always true?

1. LASTIN = LASTPOST
2. LASTIN = LASTPRE
3. LASTPRE = LASTPOST
4. None of these

Solution-

Consider the following complete binary tree-

Preorder Traversal  : B , A , E

Inorder Traversal     : B , A , E

Postorder Traversal : B , E , A

Clearly, LASTIN = LASTPRE.

Thus, Option (B) is correct.

Problem-04:

Which of the following binary trees has its inorder and preorder traversals as BCAD and ABCD respectively-

Solution-

Option (D) is correct.

To watch video solutions and practice more problems,

Watch this Video Lecture

Next Article- Binary Search Trees

Get more notes and other study material of Data Structures.

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Binary Tree-

Before you go through this article, make sure that you gone through the previous article on Binary Trees.

We have discussed-

• Binary tree is a special tree data structure.
• In a binary tree, each node can have at most 2 children.
• There are following types of binary trees-

In this article, we will discuss properties of binary trees.

Binary Tree Properties-

Important properties of binary trees are-

Property-01:

 Minimum number of nodes in a binary tree of height H= H + 1

Example-

To construct a binary tree of height = 4, we need at least 4 + 1 = 5 nodes.

Property-02:

 Maximum number of nodes in a binary tree of height H= 2H+1 – 1

Example-

Maximum number of nodes in a binary tree of height 3

= 23+1 – 1

= 16 – 1

= 15 nodes

Thus, in a binary tree of height = 3, maximum number of nodes that can be inserted = 15.

We can not insert more number of nodes in this binary tree.

Property-03:

 Total Number of leaf nodes in a Binary Tree= Total Number of nodes with 2 children + 1

Example-

Consider the following binary tree-

Here,

• Number of leaf nodes = 3
• Number of nodes with 2 children = 2

Clearly, number of leaf nodes is one greater than number of nodes with 2 children.

This verifies the above relation.

NOTE

It is interesting to note that-

Number of leaf nodes in any binary tree depends only on the number of nodes with 2 children.

Property-04:

 Maximum number of nodes at any level ‘L’ in a binary tree= 2L

Example-

Maximum number of nodes at level-2 in a binary tree

= 22

= 4

Thus, in a binary tree, maximum number of nodes that can be present at level-2 = 4.

To gain better understanding about Binary Tree Properties,

Watch this Video Lecture

Problem-01:

A binary tree T has n leaf nodes. The number of nodes of degree-2 in T is ______?

1. log2n
2. n-1
3. n
4. 2n

Solution-

Using property-3, we have-

Number of degree-2 nodes

= Number of leaf nodes – 1

= n – 1

Thus, Option (B) is correct.

Problem-02:

In a binary tree, for every node the difference between the number of nodes in the left and right subtrees is at most 2. If the height of the tree is h > 0, then the minimum number of nodes in the tree is ______?

1. 2h-1
2. 2h-1 + 1
3. 2h – 1
4. 2h

Solution-

Let us assume any random value of h. Let h = 3.

Then the given options reduce to-

1. 4
2. 5
3. 7
4. 8

Now, consider the following binary tree with height h = 3-

• This binary tree satisfies the question constraints.
• It is constructed using minimum number of nodes.

Thus, Option (B) is correct.

Problem-03:

In a binary tree, the number of internal nodes of degree-1 is 5 and the number of internal nodes of degree-2 is 10. The number of leaf nodes in the binary tree is ______?

1. 10
2. 11
3. 12
4. 15

Solution-

Using property-3, we have-

Number of leaf nodes in a binary tree

= Number of degree-2 nodes + 1

= 10 + 1

= 11

Thus, Option (B) is correct.

Problem-04:

The height of a binary tree is the maximum number of edges in any root to leaf path. The maximum number of nodes in a binary tree of height h is ______?

1. 2h
2. 2h-1 – 1
3. 2h+1 – 1
4. 2h+1

Solution-

Using property-2, Option (C) is correct.

Problem-05:

A binary tree T has 20 leaves. The number of nodes in T having 2 children is ______?

Solution-

Using property-3, correct answer is 19.

To watch video solutions and practice more problems,

Watch this Video Lecture

Next Article- Binary Tree Traversal

Get more notes and other study material of Data Structures.

Watch video lectures by visiting our YouTube channel LearnVidFun.

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.

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.

Unlabeled Binary Tree-

 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 3C3 / (3 + 1)

6C3 / 4

= 5

Thus,

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

Labeled Binary Tree-

 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 3C3 / (3 + 1) } x 3!

= { 6C3 / 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-

1. Rooted Binary Tree
2. Full / Strictly Binary Tree
3. Complete / Perfect Binary Tree
4. Almost Complete Binary Tree
5. 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.

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-

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-

Watch this Video Lecture

Also Read- Binary Tree Traversal