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Hi! I'm Eric Wastl. I make Advent of Code. I hope you like it! I also make lots of other things. I'm on Bluesky, Mastodon, and GitHub.
Advent of Code is an Advent calendar of small programming puzzles for a variety of skill levels that can be solved in any programming language you like. People use them as interview prep, company training, university coursework, practice problems, a speed contest, or to challenge each other.
You don't need a computer science background to participate - just a little programming knowledge and some problem solving skills will get you pretty far. Nor do you need a fancy computer; every problem has a solution that completes in at most 15 seconds on ten-year-old hardware.
If you'd like to support Advent of Code, you can do so indirectly by helping to it with others or directly via AoC++.
--- General Tips ---
If you get stuck, try your solution against the examples given in the puzzle; you should get the same answers. If not, re-read the description. Did you misunderstand something? Is your program doing something you don't expect? After the examples work, if your answer still isn't correct, build some test cases for which you can verify the answer by hand and see if those work with your program. Make sure you have the entire puzzle input. If you're still stuck, maybe ask a friend for help, or come back to the puzzle later. You can also ask for hints in the subreddit.
--- Frequently Asked Questions ---
Is there an easy way to select entire code blocks? You should be able to triple-click code blocks to select them. You'll need JavaScript enabled.
#!/usr/bin/env perl use warnings; use strict; print "You can test it out by "; print "triple-clicking this code.\n";How does authentication work? Advent of Code uses OAuth to confirm your identity through other services. When you log in, you only ever give your credentials to that service - never to Advent of Code. Then, the service you use tells the Advent of Code servers that you're really you. In general, this reveals no information about you beyond what is already public; here are examples from Reddit and GitHub. Advent of Code will remember your unique ID, names, URL, and image from the service you use to authenticate.
Why was this puzzle so easy / hard? The difficulty and subject matter varies throughout each event. Very generally, the puzzles get more difficult over time, but your specific skillset will make each puzzle significantly easier or harder for you than someone else. Making puzzles is tricky.
Why do the puzzles unlock at midnight EST/UTC-5? Because that's when I can consistently be available to make sure everything is working. I also have a family, a day job, and even need sleep occasionally. If you can't participate at midnight, that's not a problem; if you want to race, many people use private leaderboards to compete with people in their area.
I find the text on the site hard to read. Is there a high contrast mode? There is a high contrast alternate stylesheet. Firefox supports these by default (View -> Page Style -> High Contrast).
I have a puzzle idea! Can I send it to you? Please don't. Because of legal issues like copyright and attribution, I don't accept puzzle ideas, and I won't even read your email if it looks like one just in case I use parts of it by accident.
Did I find a bug with a puzzle? Once a puzzle has been out for even an hour, many people have already solved it; after that point, bugs are very unlikely. Start by asking on the subreddit.
Should I try to get a fast solution time? Maybe. Solving puzzles is hard enough on its own, but trying for a fast time also requires many additional skills and a lot of practice; speed-solves often look nothing like code that would pass a code review. If that sounds interesting, go for it! However, you should do Advent of Code in a way that is useful to you, and so it is completely fine to choose an approach that meets your goals and ignore speed entirely.
Why did the number of days per event change? It takes a ton of my free time every year to run Advent of Code, and building the puzzles accounts for the majority of that time. After keeping a consistent schedule for ten years(!), I needed a change. The puzzles still start on December 1st so that the day numbers make sense (Day 1 = Dec 1), and puzzles come out every day (ending mid-December).
What happened to the global leaderboard? The global leaderboard was one of the largest sources of stress for me, for the infrastructure, and for many users. People took things too seriously, going way outside the spirit of the contest; some people even resorted to things like DDoS attacks. Many people incorrectly concluded that they were somehow worse programmers because their own times didn't compare. What started as a fun feature in 2015 became an ever-growing problem, and so, after ten years of Advent of Code, I removed the global leaderboard. (However, I've made it so you can share a read-only view of your private leaderboard. Please don't use this feature or data to create a "new" global leaderboard.)
While trying to get a fast time on a private leaderboard, may I use AI / watch streamers / check the solution threads / ask a friend for help / etc? If you are a member of any private leaderboards, you should ask the people that run them what their expectations are of their members. If you don't agree with those expectations, you should find a new private leaderboard or start your own! Private leaderboards might have rules like maximum runtime, allowed programming language, what time you can first open the puzzle, what tools you can use, or whether you have to wear a silly hat while working.
Should I use AI to solve Advent of Code puzzles? No. If you send a friend to the gym on your behalf, would you expect to get stronger? Advent of Code puzzles are designed to be interesting for humans to solve - no consideration is made for whether AI can or cannot solve a puzzle. If you want practice prompting an AI, there are almost certainly better exercises elsewhere designed with that in mind.
Can I copy/redistribute part of Advent of Code? Please don't. Advent of Code is free to use, not free to copy. If you're posting a code repository somewhere, please don't include parts of Advent of Code like the puzzle text or your inputs. If you're making a website, please don't make it look like Advent of Code or name it something similar.
--- Credits ---
Puzzles, Code, & Design: Eric Wastl
Beta Testing:
- Tim Giannetti
- Ben Lucek
- JP Burke
- Aneurysm9
- Andrew Skalski
Community Managers: Danielle Lucek and Aneurysm9
Playing: You!
--- Legal ---
Advent of Code is a registered trademark in the United States. The design elements, language, styles, and concept of Advent of Code are all the sole property of Advent of Code and may not be replicated or used by any other person or entity without express written consent of Advent of Code. Copyright 2015-2025 Advent of Code. All rights reserved.
You may link to or reference puzzles from Advent of Code in discussions, classes, source code, printed material, etc., even in commercial contexts. Advent of Code does not claim ownership or copyright over your solution implementation.
