Data Structure Java Interview Questions

A data structure is an important building block of computer programming. It is the most basic and fundamental concept that every programmer or developer starts with when they decide to learn to programme or choose to programme as a hoppy or career option.

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For Java programming language, the application of data structure is huge in any project, solution or product. The success of a product, scalability, and extensibility of its scope is highly dependent on the type of data structure chosen for various tasks and components during software development.

In this Data Structure Java Interview Questions article, we shall provide important data structure questions to help candidates improve his/her skill on a subject.

If you are looking for a job related to Data Structure Java, you need to prepare for the 2023 Data Structure Java Interview Questions. Every interview is indeed different as per the different job profiles. Here, we have prepared the important Data Structure Java Interview Questions and Answers, which will help you succeed in your interview.

In this 2023 Data Structure Java Interview Questions article, we shall present the 10 most important and frequently asked Data Structure Java interview questions. These interview questions are divided into two parts are as follows:

Part 1 – Data Structure Java Interview Questions (Basic)

This first part covers basic Interview Questions and Answers.

Q1. How do you find the middle element of the linked list in one pass?

Answer:
In order to find the middle element of the linked list in one pass, one needs to maintain a two-pointer. One of these pointers will increment at each node while the other will increment after two nodes simultaneously; thus, by having this type of arrangement, when the first pointer reaches the end of the linked list, the second pointer will point to a middle element of the linked list.

Q2. How to know if a linked list has a loop?

Answer:
If two pointers are maintained, and one of them is incremented after processing two nodes and the other after processing every node, it is likely that we find a situation where both the pointers are pointed to the same node.
This happens only if a linked list consists of a loop or cycle.

Let us move to the next Data Structure Java Interview Questions.

Q3. How to identify the third element from the end in a linked list in one pass?

Answer:
If the same trick as above of maintaining two pointers is applied where one pointer increments, when first has moved up to the 3rd element, then in that case when the first pointer reaches to the end of the given linked list, the second pointer will be pointing to the 3rd element of the list from last.

Q4. How to find a duplicate number in an integer array between 1 to 100 numbers?

Answer:
These are the common Data Structure Java Interview Questions asked in an interview. To get the answer, one can simply add all numbers stored in that particular array, and the total sum should be equal to n(n+1)/2. After this, one should subtract the actual sum to the expected sum, and that is how duplicate numbers can be found.

Q5. How to reverse String in Java language?

Answer:
There are many ways available to reverse String in Java or other programming languages; one could do so by using built-in functions such as reverse() from the StringBuffer class.

Part 2 – Data Structure Java Interview Questions (Advanced)

Let us now have a look at the advanced Interview Questions and Answers.

Q6. Describe some of the operations that are performed on different Data Structures?

Answer:
Operations that can be performed on data structures are as below:

• Insertion: This is used to add a new data item in the existing set of data items.
• Deletion: This is used to delete an already available data item from the existing set of data items.
• Traversal: This can be used to access each data item only once before it is processed.
• Searching: This can be used to find out the location of the data item if that particular item exists in the given collection of data items.
• Sorting: This one is for arranging the data items in some order, such as in ascending or descending order of numerical data and in dictionary order if alphanumeric data.

Q7. What do you understand by a Linked List, and What are its different types?

Answer:
A linked list can be regarded as a linear data structure, where each element is considered as a separate object or entity in itself. Each element within a list consists of two items – the data and the reference to the next node.

Types of Linked List:

• Singly Linked List: In a singly linked list, every node stores two pieces of information. One is the address of the next node, and the other is data. The last node has NULL.
• Doubly Linked List: In a doubly-linked list, there are two references to each node, a reference to the next node and to the previous node.
• Circular Linked List: In a circular linked list, all nodes are connected to each other and hence no NULL at the end. A circular linked list can be singly circular or doubly circular.

Q8. What do you understand by Data Structure?

Answer:
A data structure can be considered as a way of organizing the data for efficient utilization.

For example, Binary trees are particularly suited for database implementation, while compiler implementations are usually done using hash tables to look up identifiers.

Q9. What are linear and non-linear types of data Structures? Also, How is an Array different from Linked List?

Answer:

• Linear: A data structure is called as linear if its elements form a sequence or a linear list such as Array, Linked List, Stacks, and Queues.
• Non-Linear: A data structure is non-linear if the traversal of nodes is nonlinear in nature, such as Graphs and Trees.

The difference between array and linked list are the following: –

• The size of the arrays is always fixed; linked Lists size is not fixed.
• Insert and delete in an array is an expensive process, whereas the same can be easily done in Linked Lists.
• Accessing an element randomly is not possible in the case of Linked Listed but is possible in an array.
• Extra memory space for a pointer is needed with each element of the Linked list; arrays don’t have pointers.
• Arrays have a better cache locality mechanism that can make a big difference in performance.

Q10. What do you understand by Stack, and where can it be used?

Answer:
This is the most popular Data Structure Java Interview Questions asked in an interview. A stack can be understood as a linear data structure that uses the order LIFO (Last In First Out) or FILO (First In Last Out) for accessing its elements. Basic operations on a stack are: Push, Pop and Peek.

Applications of Stack are following:

• Infix to Postfix Conversion can be done using Stack.
• Evaluation of Postfix Expression is also possible.
• Reverse a String using Stack can be done.
• Implement two stacks in an array is also a nice use case.
• Check for balanced parentheses in an expression is done using stacks.

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