Problem 074

btilly · Post by **btilly** » Fri Sep 26, 2008 8:02 am

I have what I really believe is the right answer, and I've verified my code every way I can, but it won't accept my answer. Yes, I know that the natural first reaction is to assume that I need to check again and am wrong, but given that I've successfully solved 76 problems in 3 days, and I've been double-checking this one for over an hour with no sign of a possible problem, I am seriously considering the possibility that the problem is with PE's answer and/or question. (I know that wording of questions sometimes changes..)

Can someone verify for me that the starts of the chains of length 60 are all the permutations of snip!, or else tell me a start of a chain that I am missing?

jaap · Post by **jaap** » Fri Sep 26, 2008 8:33 am

Try 1479 or snip!.

harryh · Post by **harryh** » Fri Sep 26, 2008 8:57 am

I had to snip a couple of values - since they seemed to be giving away almost all of the possibilities.
And there is no error in the answer to this problem as entered in the database - I doublechecked.

btilly · Post by **btilly** » Fri Sep 26, 2008 9:14 am

jaap wrote:Try 1479 or snip!.

D'oh! 1! is not 0.

jaap · Post by **jaap** » Fri Sep 26, 2008 10:17 am

harryh wrote:I had to snip a couple of values - since they seemed to be giving away almost all of the possibilities.

Sorry about that, I didn't notice. Thanks.

exelian · Post by **exelian** » Mon Oct 13, 2008 7:58 pm

I found some errors in the calculation presented as example in problem 74. The first proposed sequence is said to be:
169 -> 363601 -> 1454 -> 169.
But it turns out 3! + 6! + 3! + 6! + 0! + 1! = 1453, making the whole example invalid.
The other 2 examples are correct, maybe this should be corrected.

I could of course be entirely wrong, in which case I wouldn't mind some enlightenment on the problem.

daniel.is.fischer · Post by **daniel.is.fischer** » Mon Oct 13, 2008 8:06 pm

The thing is that 0! = 1. So 3! + 6! + 3 ! + 6! + 0! + 1! = 6 + 720 + 6 + 720 + 1 + 1 = 1454.
There are very good reasons for 0! = 1, so much so that it's the only reasonable definition of 0!.

exelian · Post by **exelian** » Mon Oct 13, 2008 8:19 pm

Ah, of course, I knew there must've been something I'd missed, back to problem solving I guess.

jaap · Post by **jaap** » Mon Oct 13, 2008 8:20 pm

daniel.is.fischer wrote:The thing is that 0! = 1. So 3! + 6! + 3 ! + 6! + 0! + 1! = 6 + 720 + 6 + 720 + 1 + 1 = 1454.
There are very good reasons for 0! = 1, so much so that it's the only reasonable definition of 0!.

See for example this recent post of mine.

Project Euler Forum

Problem 074

Problem 074

Re: Can someone verify problem 74?

Re: Can someone verify problem 74?

Re: Can someone verify problem 74?

Re: Can someone verify problem 74?

Problem 74

Re: Errors in problem 74

Re: Errors in problem 74

Re: Errors in problem 74