Questions on Binary Search Tree

Tag: Questions on Binary Search Tree

Binary Search Tree Traversal | BST Traversal

Binary Search Tree-

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

Binary search tree (BST) is a special kind of binary tree where each node contains-

Only larger values in its right subtree.
Only smaller values in its left subtree.

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

BST Traversal-

A binary search tree is traversed in exactly the same way a binary tree is traversed.
In other words, BST traversal is same as binary tree traversal.

Read More- Binary Tree Traversal

Example-

Consider the following binary search tree-

Now, let us write the traversal sequences for this binary search tree-

Preorder Traversal-

100 , 20 , 10 , 30 , 200 , 150 , 300

Inorder Traversal-

10 , 20 , 30 , 100 , 150 , 200 , 300

Postorder Traversal-

10 , 30 , 20 , 150 , 300 , 200 , 100

Important Notes-

Note-01:

Inorder traversal of a binary search tree always yields all the nodes in increasing order.

Note-02:

Unlike Binary Trees,

A binary search tree can be constructed using only preorder or only postorder traversal result.
This is because inorder traversal can be obtained by sorting the given result in increasing order.

To gain better understanding about Binary Search Tree Traversal,

Watch this Video Lecture

PRACTICE PROBLEMS BASED ON BST TRAVERSAL-

Problem-01:

Suppose the numbers 7 , 5 , 1 , 8 , 3 , 6 , 0 , 9 , 4 , 2 are inserted in that order into an initially empty binary search tree. The binary search tree uses the usual ordering on natural numbers.

What is the inorder traversal sequence of the resultant tree?

7 , 5 , 1 , 0 , 3 , 2 , 4 , 6 , 8 , 9
0 , 2 , 4 , 3 , 1 , 6 , 5 , 9 , 8 , 7
0 , 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9
9 , 8 , 6 , 4 , 2 , 3 , 0 , 1 , 5 , 7

Solution-

This given problem may be solved in the following two ways-

Method-01:

We construct a binary search tree for the given elements.
We write the inorder traversal sequence from the binary search tree so obtained.

Following these steps, we have-

Thus, Option (C) is correct.

Method-02:

We know, inorder traversal of a binary search tree always yields all the nodes in increasing order.

Using this result,

We arrange all the given elements in increasing order.
Then, we report the sequence so obtained as inorder traversal sequence.

Inorder Traversal :

0 , 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9

Thus, Option (C) is correct.

Problem-02:

The preorder traversal sequence of a binary search tree is-

30 , 20 , 10 , 15 , 25 , 23 , 39 , 35 , 42

What one of the following is the postorder traversal sequence of the same tree?

10 , 20 , 15 , 23 , 25 , 35 , 42 , 39 , 30
15 , 10 , 25 , 23 , 20 , 42 , 35 , 39 , 30
15 , 20 , 10 , 23 , 25 , 42 , 35 , 39 , 30
15 , 10 , 23 , 25 , 20 , 35 , 42 , 39 , 30

Solution-

In this question,

We are provided with the preorder traversal sequence.
We write the inorder traversal sequence by arranging all the numbers in ascending order.

Then-

Postorder Traversal : 30 , 20 , 10 , 15 , 25 , 23 , 39 , 35 , 42
Inorder Traversal : 10 , 15 , 20 , 23 , 25 , 30 , 35 , 39 , 42

Now,

We draw a binary search tree using these traversal results.
The binary search tree so obtained is as shown-

Now, we write the postorder traversal sequence-

Postorder Traversal :

15 , 10 , 23 , 25, 20, 35, 42, 39, 30

Thus, Option (D) is correct.

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Next Article- Binary Search Tree Operations

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Binary Search Tree | Example | Construction

Data Structures

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 a binary tree, nodes may be arranged in any random order.

In this article, we will discuss about Binary Search Trees.

Binary Search Tree-

Binary Search Tree is a special kind of binary tree in which nodes are arranged in a specific order.

In a binary search tree (BST), each node contains-

Only smaller values in its left sub tree
Only larger values in its right sub tree

Example-

Number of Binary Search Trees-

Example-

Number of distinct binary search trees possible with 3 distinct keys

= ^2×3C₃ / 3+1

= ⁶C₃ / 4

= 5

If three distinct keys are A, B and C, then 5 distinct binary search trees are-

Binary Search Tree Construction-

Let us understand the construction of a binary search tree using the following example-

Example-

Construct a Binary Search Tree (BST) for the following sequence of numbers-

50, 70, 60, 20, 90, 10, 40, 100

When elements are given in a sequence,

Always consider the first element as the root node.
Consider the given elements and insert them in the BST one by one.

The binary search tree will be constructed as explained below-

Insert 50-

Insert 70-

As 70 > 50, so insert 70 to the right of 50.

Insert 60-

As 60 > 50, so insert 60 to the right of 50.
As 60 < 70, so insert 60 to the left of 70.

Insert 20-

As 20 < 50, so insert 20 to the left of 50.

Insert 90-

As 90 > 50, so insert 90 to the right of 50.
As 90 > 70, so insert 90 to the right of 70.

Insert 10-

As 10 < 50, so insert 10 to the left of 50.
As 10 < 20, so insert 10 to the left of 20.

Insert 40-

As 40 < 50, so insert 40 to the left of 50.
As 40 > 20, so insert 40 to the right of 20.

Insert 100-

As 100 > 50, so insert 100 to the right of 50.
As 100 > 70, so insert 100 to the right of 70.
As 100 > 90, so insert 100 to the right of 90.

This is the required Binary Search Tree.

To gain better understanding about Binary Search Trees,

Watch this Video Lecture

PRACTICE PROBLEMS BASED ON BINARY SEARCH TREES-

Problem-01:

A binary search tree is generated by inserting in order of the following integers-

50, 15, 62, 5, 20, 58, 91, 3, 8, 37, 60, 24

The number of nodes in the left subtree and right subtree of the root respectively is _____.

(4, 7)
(7, 4)
(8, 3)
(3, 8)

Solution-

Using the above discussed steps, we will construct the binary search tree.

The resultant binary search tree will be-

Clearly,

Number of nodes in the left subtree of the root = 7
Number of nodes in the right subtree of the root = 4

Thus, Option (B) is correct.

Problem-02:

How many distinct binary search trees can be constructed out of 4 distinct keys?

Solution-

Number of distinct binary search trees possible with 4 distinct keys

= ²ⁿC_n / n+1

= ^2×4C₄ / 4+1

= ⁸C₄ / 5

= 14

Thus, Option (B) is correct.

Problem-03:

The numbers 1, 2, …, n are inserted in a binary search tree in some order. In the resulting tree, the right subtree of the root contains p nodes. The first number to be inserted in the tree must be-

p
p+1
n-p
n-p+1

Solution-

Let n = 4 and p = 3.

Then, given options reduce to-

Our binary search tree will be as shown-

Clearly, first inserted number = 1.

Thus, Option (C) is correct.

Problem-04:

We are given a set of n distinct elements and an unlabeled binary tree with n nodes. In how many ways can we populate the tree with given set so that it becomes a binary search tree?

0
1
n!
C(2n, n) / n+1

Solution-

Option (B) is correct.

To watch video solutions and practice more problems,

Watch this Video Lecture

Download Handwritten Notes Here-

Next Article- Binary Search Tree Traversal

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