Algorithms

What people mean — and don't mean — by 'the algorithm'

A recipe is an algorithm. A feed ranking your friends is a lot of them stacked up.

Interactive14 minComputingCitizenship

What people mean — and don't mean — by 'the algorithm' — illustration

A precise definition

An algorithm is a finite sequence of unambiguous steps that solves a problem. Sequence, selection and iteration are enough to build almost any of them.

Comparing two that do the same job

Linear search checks every item; binary search halves the list each time but needs it sorted. On a million items that is a million checks versus about twenty.

Ranking feeds

A recommendation system scores each post against signals — recency, engagement, similarity to what you watched. 'The algorithm' is a scoring rule, written by people who chose those signals.

Check your understanding

1. Which best defines an algorithm?

2. Binary search needs the list to be…

3. What is 'the algorithm' in a social feed?

Your turn

Write binary search as numbered steps, then trace it on a list of sixteen numbers.

Luna: Only if you feel up to it — one more?

Ask the AI tutor

Curriculum objectives covered

Understand several key algorithms, including those for sorting and searching
Understand simple algorithms expressed using sequence, selection and iteration