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Beginner Topic 7 of 51 Algorithms

Binary Search

Halving a sorted range repeatedly to locate a target.

How it works

On a sorted array, compare the target with the middle element and discard half the range each step: O(log n). 1 billion items need only about 30 comparisons.

Where it is used

Dictionary lookup, finding insertion points, searching answer spaces ("binary search on the answer").

Common pitfall

Off-by-one errors in bounds, overflow in (lo+hi)/2 (use lo + (hi-lo)/2), and applying it to unsorted data.

Where it fits in the course

Binary Search is topic 7 of 51 in Algorithms, rated Beginner. It follows Linear Search. The next topic is Bubble Sort.

Practice and explore

How to study this topic

  1. Read the explanation above and restate the definition in your own words.
  2. Open the interactive lesson and answer its mini quiz.
  3. Read the common pitfall, then write a short example that avoids it.
  4. Check your understanding in the Algorithms quiz, and revisit the topic if you miss a question.

Frequently asked questions

What is Binary Search?
Halving a sorted range repeatedly to locate a target. It belongs to Algorithms and is a beginner-level topic.
Where do people use Binary Search?
Dictionary lookup, finding insertion points, searching answer spaces ("binary search on the answer").
What is the most common mistake with Binary Search?
Off-by-one errors in bounds, overflow in (lo+hi)/2 (use lo + (hi-lo)/2), and applying it to unsorted data.
What should I learn before this topic?
Start with Linear Search, 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 Linear vs Binary Search in the Visual Lab.
Is Binary Search 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 Binary Search?
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 Binary Search?
Linear Search, Bubble Sort, Big-O Notation are closely connected. The full list is in the related topics section of this page.
What should I study after Binary Search?
Continue with Bubble Sort, the next topic in Algorithms.

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