ELI5: explai time complexity and space complexity

What is time complexity?

Time complexity is like measuring how long it takes to do a job. [5] If you have to count 10 toys, it takes a little while, but if you have to count 1,000 toys the same way, it takes much longer—and we want to know how much longer. [5] We use Big O notation to describe this, which is like saying "this job takes about this much time." [3]

What is space complexity?

Space complexity is about how much space or memory your program needs to work, like how much desk space you need to organize your toys. [4] If you're organizing 10 toys you need a little desk space, but organizing 1,000 toys might need a much bigger desk. [4]

Why do they matter?

If you write a program that works slowly or uses tons of memory, it won't work well when you have lots of data. [3] Think of it like a recipe—some recipes are quick and easy, but others take forever and dirty every dish in the kitchen. [5]

How do you measure them?

We use Big O notation to give these a shorthand name, ignoring the less important parts to focus on what really matters when you have huge amounts of data. [2][3]