EasyDSA12 min read

What is the difference between an array and a linked list?

Q: What is the difference between an array and a linked list?

**Target Audience:** Beginners learning data structures — no prior knowledge assumed. **Difficulty:** Easy **Language:** Python 3 > **How to read this doc:** Each idea is explained in plain language first, then tagged with `📌 Interview term:` so you also learn the exact words an interviewer expects. Every program in this doc was run with `python3 main.py`, and the output quoted in the **Verified** section is copied from that run. ## 1. Why This Even Matters — A Story First Picture two ways of storing a class's homework. In the first, every notebook goes into a row of numbered lockers, side by side: if you want notebook number 37, you walk straight to locker 37. But if a new student must go in at locker 1, everyone in lockers 1 to 40 has to move one locker to the right. In the second, the notebooks are spread all over the school, and each one has a sticky note saying where the next one is. Adding a new first notebook is easy: write a sticky note pointing to the old first one, and y

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The problem

Question presented to candidate: "Explain the difference between an array and a linked list. When would you pick one over the other, and what does each look like in Python? If there is time, sketch a small linked list in Python."

What a strong answer should cover:

Memory layout: one contiguous block versus separate nodes joined by references.
Costs: O(1) indexing versus O(n) walking; O(n) front inserts versus O(1) relinking at a node you already hold (and that finding the node is still O(n)).
Dynamic arrays and amortized O(1) appends; the extra memory per node in a linked list.
Cache locality as the practical reason arrays usually win.
Python specifics: list is a dynamic array (of references), the standard library has no linked list class, and collections.deque is the tool for O(1) work at both ends.

Code / implementation expected: Optional — a small Node class with insert, delete and traversal in Python is a common follow-up.

arrays
linked-list

Try it yourself

Sketch your approach before you read the solution. That is what the interview tests.

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A short nudge toward the approach. It will not give the answer away.

Solution

Target Audience: Beginners learning data structures — no prior knowledge assumed. Difficulty: Easy Language: Python 3

How to read this doc: Each idea is explained in plain language first, then tagged with 📌 Interview term: so you also learn the exact words an interviewer expects. Every program in this doc was run with python3 main.py, and the output quoted in the Verified section is copied from that run.

1. Why This Even Matters — A Story First

Picture two ways of storing a class's homework. In the first, every notebook goes into a row of numbered lockers, side by side: if you want notebook number 37, you walk straight to locker 37. But if a new student must go in at locker 1, everyone in lockers 1 to 40 has to move one locker to the right.

In the second, the notebooks are spread all over the school, and each one has a sticky note saying where the next o

The solution is hidden so you can try first

12 min read · 14 sections

Python code

Edit the code and run it here. Each printed line with an expected value becomes a test.

PythonCounting the work: array moves vs list hops

Practice

PythonA singly linked list from scratch

Practice

Discussion

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