Problem 421

[Anton_Lunyov]

The problem seems easy.
I solved it in about 58 minutes.
And there is 30 minutes I can't find bug from that time.
I add a lot of cross-checks to verify that the program works fine.
Also absence of solvers make me feel like answer in the system is incorrect.

Edit: My answer is ___*************___ [edited by euler - the 3-digits you provided at front and back were correct].
All are welcome to confirm this

[epiclolz]

same here, i've replaced everything with long longs, and checked the test cases, did some checks of bits of the program, everything seems fine

edit: solve time for me was somewhere between 1.5 and 2 hours, assuming my answer is actually correct... if this makes any difference :p

[tec]

same here. solved in 1.5~2h, and keep finding errors, checking for overflow, etc.
2h50m after problem publish now and still no solvers.

[aleksey]

Same here.

[x22]

Same here.

[ignat_s]

I daresay, "same here". Though it took me much longer, about 3hr 40 min to get the answer that I think is correct.

[mihassan]

Can anyone please confirm the answer for a smaller case?
∑ s(n,10^3) for 1<= n<=10^6 = 631960606

[euler]

I think I found the problem. If you're convinced you have solved it then please try entering your answer again.

[ffff0]

Does s(1,10^8)=2?

[epiclolz]

Hello Euler/admins,

thanks for fixing the problem... I feel it is somewhat unfair though, for people who are concerned about being fast solvers. Maybe you should make it so that this problem doesn't count towards the Eulerians ranking? And freeze our points for a week :p See what everyone else thinks

[hk]

See my post in the forum.

I'm sorry to have caused problems with a leading space in the answer.
My only excuse for not fixing it earlier (and letting euler do the job) is the unghastly hour of publication (4am) (and the switch to daylight saving time over here).
For those in another time zone: those unpleasant hours are there for your benefit, so please accept the possible consequences lightheartedly.

@epiclolz:
In my opinion it's all in the game that sometimes something goes wrong, so please keep it at accepting apologies, and don't start fishing for measures.

[thundre]

Does s(1,10^8)=2?

Yes.

[Francky]

Perhaps, it is possible to find in /tmp, some correct answers and manually give back the "honor" to first solvers.
It's not a problem for me as I solved it much later... and it's true sometimes things goes wrong...
PE stay for me a very high quality place. It's always a pleasure to solve one (when I'm able to).
It is my best rank here (30th) in about 3 hours of work. (Also thanks for the new awards, some of my posts for easy problems seem to gave me some points, but for recent problems I feel unable to give for now quality posts.)
---
edit : it seems times are changing, so it is possible that things will come in order. Well done.

[sivakd]

Actually, as per viewtopic.php?f=5&t=3161#p33800 euler mentioned that all the answers entered are being persisted. So, it should be possible to accurately get the rankings and solved timings.

[rng_58]

Yesterday I solved this problem. I made several attempts around 30-50 minutes after the problem was published. Initially my solution contained bugs, but my third attempt was a correct solution. I made more attempts after the correct solution (because the judge said it's wrong).

Today I came here, submitted the same answer again, and got accepted. Could you check the database?

[euler]

@rng_58: Unfortunately there is no record of submission times for any members. As I said in the post at the top of the thread for problem 421 at Project Euler, I used the timestamps of the posts made here along with a correct submission being made a short time after the answer field was fixed to reconstruct the timeline for the Fastest Solvers table. Please check out that post for most information.

It's not going to help you now, and we certainly hope that nothing like this ever happens again, but we do not plan for these types of mini-disasters and cannot rule out an issue in the future which prevents correct answers from being submitted. So if it does happen again - that is, it becomes clear after a period of time that NO ONE is able to solve the problem - then either make a post here or send me a PM via the contact system at Project Euler with your answer. Obviously I shouldn't be receiving messages if one or two other member have successfully solved it.

[Thierry]

Can anyone please confirm the answer for a smaller case?
∑ s(n,10^3) for 1<= n<=10^6 = 631960606

I found the same result as You ... but my code is unfortunately still too slow to reach the goal ...

[jpatou]

Can anyone please confirm the answer for a smaller case?
∑ s(n,10^3) for 1<= n<=10^6 = 631960606

I found the same result as You ... but my code is unfortunately still too slow to reach the goal ...

I found 567377244 for these values.
Can someone confirm I'm wrong ?

[mihassan]

Can anyone please confirm the answer for a smaller case?
∑ s(n,10^3) for 1<= n<=10^6 = 631960606

I found the same result as You ... but my code is unfortunately still too slow to reach the goal ...

I found 567377244 for these values.
Can someone confirm I'm wrong ?

I can confirm that 631960606 is correct as I have solved the problem. Thanks Thierry for confirming, my program was also very slow initially. I think that is the challenge, how to solve the problem in a reasonable time.

[jpatou]

Thanks. I fixed my bug and I find the same result.