Beginner Topic 13 of 51 Algorithms
Counting Sort
Non-comparison sort tallying occurrences of small integer keys.
How it works
Count how many times each key appears (keys in 0..k), compute prefix sums to get positions, then place items; runs in O(n + k) without comparisons.
Where it is used
Sorting small integer ranges such as ages or grades, a subroutine for radix sort.
Common pitfall
Memory proportional to k, so useless when the key range is huge.
Where it fits in the course
Counting Sort is topic 13 of 51 in Algorithms, rated Beginner. It follows Quick Sort. The next topic is Radix Sort.
Practice and explore
- Open the interactive lesson, with a mini quiz.
- Take the Algorithms quiz.
- Explore the Sorting Algorithms visualizer: Bubble, selection, insertion, merge and quick sort animated.
How to study this topic
- Read the explanation above and restate the definition in your own words.
- Open the interactive lesson and answer its mini quiz.
- Read the common pitfall, then write a short example that avoids it.
- Check your understanding in the Algorithms quiz, and revisit the topic if you miss a question.
Frequently asked questions
What is Counting Sort?
Non-comparison sort tallying occurrences of small integer keys. It belongs to Algorithms and is a beginner-level topic.
Where do people use Counting Sort?
Sorting small integer ranges such as ages or grades, a subroutine for radix sort.
What is the most common mistake with Counting Sort?
Memory proportional to k, so useless when the key range is huge.
What should I learn before this topic?
Start with Quick Sort, the topic just before it in Algorithms.
How can I practice it?
Answer the mini quiz in the interactive lesson, then take the Algorithms quiz. You can also explore Sorting Algorithms in the Visual Lab.
Is Counting Sort hard to learn?
It is a Beginner topic, so it works as an entry point. If the terms are new, read the explanation twice and try the visualizer before the quiz.
How long does it take to learn Counting Sort?
Most learners can read the explanation and finish the interactive lesson in under an hour. Fluency comes from applying the idea, so plan a few short practice sessions with the quiz.
Which topics are related to Counting Sort?
Quick Sort, Radix Sort, Merge Sort are closely connected. The full list is in the related topics section of this page.
What should I study after Counting Sort?
Continue with Radix Sort, the next topic in Algorithms.
Related topics
- Quick Sort (Algorithms)
- Radix Sort (Algorithms)
- Merge Sort (Algorithms)
- Brute Force (Algorithms)
- Counting Principles (Theory & Discrete Math)