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45+ Array Interview Questions You Must Practice

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Array interview questions are crucial for coding interviews. If you are preparing for your upcoming tech interview at FAANG or any other Tier-1 tech company, you should be adept at arrays. It is the second-most popular topic after Strings at most coding interviews.

Arrays are a collection of similar data items stored at contiguous memory locations. They are omnipresent, as they associate with all programming languages, including C, C++, Java, Python, Perl, and Ruby. Read on for array-based interview questions and answers and some coding problems for practice.

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Here's what we'll cover in the article:

  • Theoretical Interview Questions on Array
  • Array Interview Questions in Java for Freshers
  • Array Interview Questions in Python 
  • Array Interview Questions in JavaScript
  • Array Logical Interview Questions in PHP
  • FAQs on Array Interview Questions

Theoretical Interview Questions on Array 

Arrays are a crucial topic at FAANG+ interviews. You can expect questions around peak elements, how to reverse arrays, sort arrays, the occurrence of an integer in an array, and much more. 

You should also be prepared for some theoretical questions along with coding questions on arrays for your technical interviews. Here are some Array interview questions that interviewers often ask to check your basic understanding of the concept of arrays in data structures. 

1. What are Dynamic Arrays? How are they different from Basic Arrays?

Dynamic arrays (also known as a growable array, resizable array, mutable array, or ArrayLists in Java) offer a big improvement, i.e., automatic resizing. 

An array has a fixed size, so you always have to specify the number of elements your array will hold ahead of time. However, a dynamic array expands as you add more elements to it and you need not determine the size ahead of time.

2. What are the differences between an array and a dictionary?  

This is one frequently asked array interview question that tests your fundamentals. The main differences between arrays and dictionaries are as follows:

3. What is meant by Sparse Array?

An array of data with many elements that have a zero value is termed a sparse array. Contrastingly, a dense array has most of the elements with non-zero values. Sparse array maps integers to objects, and its indices can contain gaps. These are more memory-efficient than a HashMap.

4. What is an associative array vs. an indexed array? 

The following table enumerates the key differences between associative and indexed arrays.

5. When would you use a linked list over an array?

Linked lists can be used over arrays when:

  • You require constant-time insertions/deletions from the list, where time predictability is absolutely critical.
  • You do not know how many items the list will include. As in basic arrays, you have to re-declare and copy memory if the array size increases. 
  • You do not require random access to any elements.
  • You might have to insert items in the middle of the list as in a priority queue.

6. What are the time complexities of sorted array operations, inserting a new element in dynamic arrays, and deleting a specific element?

You must have a thorough knowledge of various operations in arrays to answer this question. 

  • sort(Object[]) works on the TimSort algorithm and gives a time complexity of O(n log(n)). The TimSort algorithm uses insertion sort and merge sort algorithms. 
  • The time complexity of inserting a new element in a dynamic array is O(N).
  • The average case time complexity of deleting a specific element is O(N) in an array.

7. Dynamic arrays were an improvement over arrays. What is an improvement over dynamic arrays?

Hashed Array Tree (HAT) is an improvement over Dynamic Arrays. It offers a large amount of unused allocated memory at a time. HATs maintain an array of separate memory fragments, also called leaves to store the data elements.

8. What are the benefits of Heap over Sorted Arrays?  

The main advantage of using Heap over Sorted Arrays is the time efficiency. While sorting an array has a high time complexity, heap operations are faster. You can use a heap to find the smallest element much faster than sorting an array. 

With Sorted Arrays, there can be two arrangements of a given set of integers after sorting. On the contrary, there can be multiple possible heaps for a given set of integers. 

You must understand the complete concept of arrays in data structures. Read more about searching an element in a sorted and rotated array and much more on the Learn platform and uplevel your tech interview prep.

Array Interview Questions in Java for Freshers

Here is a list of some most anticipated array interview questions in Java for freshers. If you are an experienced professional, you can practice these questions to brush up on your fundamentals.

  1. How would you check if the array elements are consecutive? 
  2. How would you rotate an array by P positions?
  3. Write an algorithm to count zeros in a sorted binary array.
  4. How would you count the frequency of elements? 
  5. Given an array of elements, separate the odd and even elements. 
  6. How would you find the longest common prefix in a given array of strings?
  7. Given an array, how would you find the contiguous subarray with a sum equal to a target value?
  8. How would you find permutations of an array?
  9. How would you find an element using binary search?
  10. What steps will you take to implement a stack using an array?
  11. Write a program to convert a sorted array into a balanced binary search tree. Print the result.

Learn about what are arrays in Java here.

Array Interview Questions in Python 

Top FAANG companies like Google, YouTube, IBM, Intel, and other Tier-1 tech companies use Python for programming. You must practice the following Array interview questions to ace your Python interview.

  1. Write a program to find a missing number in an array with 1-100 numbers stored. 
  2. Write a program to find multiple duplicate numbers in a given array with 1-100 numbers. 
  3. How would you find all pairs in an array of integers whose sum equals a number given? 
  4. Write a program to compare whether two arrays are equal in size or not.
  5. How would you find the largest and smallest numbers in the array?
  6. Write a program to print the array in reverse order.
  7. How would you calculate the length of an array?
  8. How would you insert an element at the end of an array?
  9. How would you insert an element at a given location in an array?
  10. Write a program to print all the even numbers in an array.
  11. Write a program to print all the odd numbers in a given array.
  12. Given two arrays, write a program to merge them.
  13. How would you find the highest frequency element in an array?
  14. How would you add two numbers using recursion?
  15. How would you merge two sorted Arrays into a single sorted array? 
  16. How would you implement 3 Stacks with one array?

For more Python interview questions, read this article. 

Array Interview Questions in JavaScript

Microsoft, Netflix, Uber, Paypal are some of the top tech companies that rely on JavaScript for several backend development processes. If you are a web developer preparing for any of these companies, you must go through the following array interview questions.

  1. How would you double elements of an array without creating additional variables using reduce?
  2. How would you destructure array elements in JavaScript?
  3. How would you remove and return the last element from an array in JavaScript?
  4. How would you empty an array in JavaScript?
  5. What are the different ways to create an array in JavaScript?
  6. What do you understand by the JavaScript Map Array function?
  7. How would you use arrays to swap variables in JS?
  8. How would you fill static values in a given array in JS?

Array Logical Interview Questions in PHP

You must know that Mark Zuckerberg used PHP to develop Facebook, and even today, PHP continues to be one of the main languages for the platform. 

Etsy and YouTube also employ PHP for backend services. If you are applying for a backend developer position, you should consider learning and practicing some PHP coding questions too. Here are some array logical interview questions in PHP.

  1. Write a program in PHP to sort an array without using a sorting function.
  2. How would you find the largest and the smallest sum for a given array without using any function?
  3. Write a program in PHP to make a grid.
  4. Write a program in PHP to find an email address using regular expressions.
  5. How would you remove duplicates in an array without using any inbuilt function?
  6. Write a function to combine two array lists by alternatingly taking elements from each list.

This completes our list of array interview questions. You must practice these and get more available on the Problems page to ace your next interview and land your dream job.

FAQs on Array Interview Questions

1. Are array interview questions difficult?

Arrays are a comparatively easier data structure topic. You should have a basic knowledge of arrays to ace array interview questions. 

2. Which is the best programming language for very large arrays?

Python with NumPy works best for solving large array interview questions. Python 3 offers automatic support for large numbers, and the default number type grows whenever necessary. You can also use math libraries available in Python.

3. Are array interview questions a part of data scientist interviews?

If you are applying for a data scientist position, you must practice some array interview questions because knowledge of algorithms and data structures is useful in data science fields.

4. How do you solve an array interview question?

To solve array interview questions, you should thoroughly brush up on your array fundamentals, including array operations (from declaring/creating an array to accessing/modifying array elements) and programming constructors such as loop, recursion, and fundamental operators.

5. How do you approach an array problem?

Understand the problem thoroughly. If you have any questions, ask for clarification. Consider breaking the problem down into smaller chunks. Before you start coding, ensure you have the algorithm in mind — jot it down or create a flowchart to picture it. Then start coding.

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