Radewoosh inspired me by completing Project Euler, and I recently started, slow but steady, solving its problems. I don't mind anybody adding me as a friend on Project Euler, my friendship key is `2127163_HmDkRoxUDZa38znoBSPq2n4Prg996WEX`

, please enter it on this page if you're registered and you'd like to see me in your friend list. (Similarly, you'll appear in my friend list.)

I also record the process and upload on Youtube because, according to the rules, problems 1–100 are allowed for public analysis (although I'm afraid there won't be any serious or interesting problems in the first hundred). As for now, uploaded are:

These are screencasts, I would even call them editorials, but (at least in the earlier problems) there isn't exactly much to explain. Watch if you like!

Finally, I really encourage you to register and solve problems as well, if you haven't still!

**UPD.** Guys, I hate to say this, but Project Euler has an obscure limit of 64 friends max. That means that I cannot add all of you in my friends list.

Therefore, I kinda have to implement some sort of preference and remove people with the lowest one. Some preferences like time of appearance in my friend list sound like trash, so we won't be considering them. Instead I decided to remove people with the fewest problems solved. Currently, at least 11 solved problems are needed. Therefore, if you got deleted and for some reason you want back, just solve a couple of problems and try adding back again!

**Spoiler**

Auto comment: topic has been updated by orz (previous revision, new revision, compare).I started grinding ~3 months ago. Right now, I'm doing it casually.

My friend key(in case anyone wants to add me)`1275826_jkyzVINq34WB3Ut8JnZOEXnvWFJ1hxlu`

The discussion threads are helpful. E.g.

Problem 10`Lucy_Hedgehog`

described an $$$O(N^{3/4})$$$ prime counting algorithm in problem 10.That technique is used in many other problems.

Well, it is even possible to do it in $$$\mathcal{O}{\left(n^{\frac{2}{3}} \log^{\frac{1}{3}}{n}\right)}$$$ time. However, for problems like tenth it is definitely an overkill.

If you want to enjoy Project Euler more, try solving some recent problems rather than just old ones.

I’ve added you in my friend list. I look forward to seeing you beat me on the recent problems!

I wanted to solve the today problem, but, for the recent problems, only getting in the first 50 solvers makes sense. And today I unfortunately felt not very well, so I decided to skip Codeforces Round 919 (Div. 2) and PE.862.

I finally managed to solve a recent problem. I woke up at 7:00 am today and I was 29

^{th}who solved Problem 874. Maximal Prime Score!Auto comment: topic has been updated by orz (previous revision, new revision, compare).Auto comment: topic has been updated by orz (previous revision, new revision, compare).Hello, your friend token is invalid

Fixed.

Project Euler grind is truly addicting, nice to see more people joining in after that blog from Radewoosh. Nothing like spending weeks on a problem generously marked by PE as "40% difficulty". Worth it, though.

My friend key for anyone interested`1477911_TuMm8yM8dRqPeSgKfG9TjouG2YPmnLwG`

I don't understand in project Euler how do you know if your approach is good enough. For example the second question (finding sum of even fibonacci numbers below 4 million) can be easily brute forced but the solution shows an expression for just finding the even numbers.

Is the problem expected to just find the answer by whatever means and then show you the better expression on the solution? How do you infer that? How do I know that I don't need a closed-form expression that find the answer on O(1)?

Well, there is a one-minute rule, which allows you to cut too slow solutions off. Beyond this:

Some problems are educational. They usually allow suboptimal solutions, and after you solve it, you can read the attached pdf with some educational stuff, like how you could solve it faster.

After you solve a problem, you have access to the corresponding thread, where people usually share their approaches; so if some of them solved the problem faster than you did, you can read how it could be done.

Apart from that, during solving the problem, the most stable way to know if your solution can be improved in general is probably your intuition, which comes with experience.

If I stuck at particular problem, how can I know what is the solution or idea of that problem??

You cannot. Well, you can search the information in the Internet, or ask your friends, or try another approach. But if nothing helps, the intended by the website admins behavior is to just skip the problem until several days or weeks have passed and you are ready to approach it with new effort.

Some problems took me about 3 years of occasional thinking

For example? 😳

I think 167 or 581

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