What Are Data Structures and Algorithms?

Two simple ideas

• A data structure is a way of storing data so it is easy to use. A Python list, a dictionary and a set are all data structures.
• An algorithm is a list of clear steps that solves a problem, like a recipe.

Think of it like this: Think of a kitchen. The shelves, jars and drawers are data structures: they decide where things are kept. The recipe is the algorithm: the steps you follow to cook. A tidy kitchen (good data structure) makes the recipe (algorithm) quick to follow.

Why should I care?

Small programs work fine however you write them. But when there is a lot of data – millions of users, songs or products – a smart choice can be the difference between one second and one hour.

Here is a tiny example. Both pieces of code check if a number is in a collection:

numbers_list = [4, 8, 15, 16, 23, 42]
numbers_set = {4, 8, 15, 16, 23, 42}

print(23 in numbers_list)   # Python checks the items one by one
print(23 in numbers_set)    # Python jumps straight to the answer

Output

True
True

Both print True, but for a million numbers the set is thousands of times faster. In this course you'll learn why, and how to pick the right tool.

What you'll learn

Tip: You only need basic Python for this course: variables, if, loops, lists, dictionaries and functions. If any of those feel shaky, have a quick look at our Learn Python tutorial first.