Interview Basics: Static vs. Dynamic Arrays

Interview Basics: Static vs. Dynamic Arrays

Arrays are one of the most basic data structures in computer science. But they form the basis of some difficult technical interview questions! So no matter where you are in your programming career, you need to be very familiar with arrays and how to use them. Read on to review the basics of static and dynamic arrays, then watch our video to get clear on the differences between them. And once you’re ready to solve some array-based technical interview questions on your own, head to Interview Practice. You’ll be able to practice solving array interview questions that have been asked at Google, LinkedIn, Apple, Uber, and Palantir. 

First Things First

Whatever programming language you choose use in an interview, make sure you know its array methods very well. Like, forwards and backwards well. Interviewers will definitely be judging you on this! If you don’t know something basic like this in the language you’ve chosen to interview with, they’ll question how well you know that language at all… Not to mention how well you can program, period. So spend some time with your language’s documentation to make sure that you’ve got a handle on its basic and advanced array methods.

Arrays

The simplest definition of an array is that it’s a data structure that contains a group of elements. In interviews, you’ll get a lot of questions about static arrays, which are the most basic implementation of this data structure. You’ll also get questions about dynamic arrays. We’re going to focus on static and dynamic arrays in this article. (You’ll also get questions about multidimensional arrays in technical interviews, which we’re going to cover in an upcoming article.)

Static Arrays

The most basic implementation of an array is a static array. A static array is a random-access data structure with a fixed size. You have to declare its size when you first initialize it. To add or remove elements from a static array, you have to create a new appropriately-sized contiguous chunk of memory. Then you have to copy the elements that you want to keep into this new array.

The good: The item lookup by index for static arrays is really quick (O(1)), and they have a very low memory footprint.

The bad: Adding elements to or deleting elements from the array is an O(n) operation, where n is the number of elements in the array. Searching the array for a particular element is also O(n). Arrays don’t allow for the quick rearrangement of their elements.

Dynamic Arrays

A dynamic array is a random-access, variable-sized list data structure that elements can be added to or removed from. They’re basically like static arrays, but with the addition of space that’s reserved for adding more elements. When dealing with a dynamic array, there are two important factors to consider. There’s the logical size of the array (the number of elements being used by the array’s contents) and its physical size (the size of the underlying array). The physical size is counted in either the number of elements the array has room for, or the number of bytes used. In a technical interview, you should use a dynamic array if you know you’ll need to add or delete information.

The good: On average, it’s quick to insert elements to the end of the dynamic array. And item lookup by index is O(1).

The bad: They don’t allow for the quick rearrangement of their elements. And they have inconsistent runtimes for adding elements to the array, so they’re not good for real-time systems.

Diving Deeper

Now that you’re clear on the basics of static and dynamic arrays, watch this video for a deeper dive on the differences between the two.

Bonus Array Joke

  1. Why did the programmer leave his job?
  2. Because he didn’t get arrays.

(Get it? Arrays, “a raise”! Stop groaning. It’s a great joke.)

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