About this challenge
Fibonacci is a easy algorithms coding challenge. It tests algorithmic thinking and complexity analysis — the kind of problem-solving that shows up constantly in technical interviews. Write your solution in the editor above, run it against the test cases, and get instant feedback — free, in your browser, no sign-up.
Show a hint & approach (spoiler)
Hint: Iterative bottom-up is O(n) time and O(1) space. Avoid naive recursion (exponential).
Keep practicing
Browse all coding challenges, or build intuition for the underlying concepts with the algorithm visualizers and the developer cheatsheets.