Search found 521 matches

by jaap
Sat Dec 15, 2018 5:48 am
Forum: Discrete Mathematics
Topic: Sorting...
Replies: 4
Views: 50

Re: Sorting...

You have re-invented the Pigeonhole sort.

The wiki page on sorting algorithms has a separate section for non-comparison integer sorts like this. Its main disadvantage is that its running time and its memory requirements depend on max, not just on n.
by jaap
Fri Nov 16, 2018 3:47 pm
Forum: Clarifications on Project Euler Problems
Topic: Problem 351
Replies: 13
Views: 4260

Re: Problem 351

If you ever need more than, say, 600MB of data, then you are probably doing it wrong. You are either using the wrong solving method, or maybe you just don't need to have all of that data in memory at the same time.
by jaap
Fri Nov 16, 2018 2:09 pm
Forum: Clarifications on Project Euler Problems
Topic: Problem 351
Replies: 13
Views: 4260

Re: Problem 351

Cheers Jaap, I'm afraid I'll have to confess my ignorance on the first question (I'll google that though). I do use vectors, yes, but I would have thought it would pose problems of efficiency too as it will take up a lot of memory. I'll try that approach over the weekend though and see what happens...
by jaap
Fri Nov 16, 2018 1:33 pm
Forum: Clarifications on Project Euler Problems
Topic: Problem 640
Replies: 5
Views: 965

Re: Problem 640

LarryBlake wrote:
Fri Nov 16, 2018 12:55 pm
@jaap, may I PM you my assumptions and a question? I believe I'm having the same difficulty tuple describes.
Sure, go ahead.
by jaap
Fri Nov 16, 2018 10:31 am
Forum: Clarifications on Project Euler Problems
Topic: Problem 351
Replies: 13
Views: 4260

Re: Problem 351

On my system and using C/C++, defining an array this size immediately causes a 'Segmentation fault' - and the number spaces required only get larger on some of the more difficult problems on PE. Am I missing something? Do you know the difference between the stack and heap memory? Do you know how to...
by jaap
Thu Nov 08, 2018 10:30 am
Forum: Clarifications on Project Euler Problems
Topic: Problem 640
Replies: 5
Views: 965

Re: Problem 640

It seems I'm having the same problem as tuple, as I get those answers too.

Edit: Solved it now. I had made an assumption that was not true in every situation, and from reading the problem's thread, many others did so too.
by jaap
Wed Oct 17, 2018 8:46 am
Forum: Number
Topic: "Fixed Points"
Replies: 5
Views: 1218

Re: "Fixed Points"

Oh, it's the unmistakable work of Raymond Smullyan. The strings we are working with are expressions. Just like an ordinary arithmetical expression like "4+5" can be evaluated to yield "9", these strings have their own type of arithmetic that can be used to evaluate them and yield another string. You...
by jaap
Tue Oct 16, 2018 6:30 am
Forum: Number
Topic: "Fixed Points"
Replies: 5
Views: 1218

Re: "Fixed Points"

kenbrooker wrote:
Mon Oct 15, 2018 9:47 pm
In this case, X is a string and X is a function, a function of itself.
In what case? In what context do you have strings that are also functions?

It is hard to tell what misunderstandings you might have if you don't show the original text that you might be misunderstanding.
by jaap
Tue Oct 02, 2018 12:36 pm
Forum: Resources
Topic: Please Help re UVa @ https://uva.onlinejudge.org
Replies: 7
Views: 1177

Re: Please Help re UVa @ https://uva.onlinejudge.org

Main.java:2: error: class aUVa100 is public, should be declared in a file named aUVa100.java It IS "declared in a file named aUVa100.java" but... I don't know the online IDE/compiler this site uses, and I don't think I can access it without becoming a member. It clearly thinks it is in a file calle...
by jaap
Mon Oct 01, 2018 7:57 am
Forum: Resources
Topic: Please Help re UVa @ https://uva.onlinejudge.org
Replies: 7
Views: 1177

Re: Please Help re UVa @ https://uva.onlinejudge.org

Maybe you need to make the class public for it to run:

Code: Select all

public class aUVa100
by jaap
Tue Sep 25, 2018 6:14 pm
Forum: News, Suggestions, and FAQ
Topic: Progress Page turned orange.
Replies: 1
Views: 773

Re: Progress Page turned orange.

See euler's post here:
viewtopic.php?f=5&t=6663#p52409
by jaap
Fri Sep 07, 2018 12:03 pm
Forum: Clarifications on Project Euler Problems
Topic: Problem 012
Replies: 99
Views: 21048

Re: Problem 012

sriramrajan wrote:
Fri Sep 07, 2018 9:04 am
My answer has 112 divisors / factors and is the first one in the series but was declared wrong.
The question is not asking for the first one with 112 divisors, but for
... the first triangle number to have over five hundred divisors?
by jaap
Sat Jul 28, 2018 11:42 am
Forum: News, Suggestions, and FAQ
Topic: Mark problems that can be figured out through math alone
Replies: 3
Views: 948

Re: Mark problems that can be figured out through math alone

There is a thread on this forum discussing which problems can be solved with paper and pencil:
viewtopic.php?f=12&t=1982
by jaap
Thu Jul 19, 2018 9:53 am
Forum: News, Suggestions, and FAQ
Topic: Add problem categories
Replies: 1
Views: 827

Re: Add problem categories

This has been asked before. Here is a previous answer:
viewtopic.php?f=5&t=3837&p=41793#p41793
by jaap
Tue Jul 10, 2018 1:49 pm
Forum: Number
Topic: an old maths olympiad question
Replies: 27
Views: 2632

Re: an old maths olympiad question

... hence $\sin 4x=\sin 3x$ implies $\sin(\pi-4x)=\sin 3x$ Nicely done. This is the trick that I missed. I thought we would have to go all the way up to $\sin(7x)$, which would be horrible. NOTE: All this in hindsight knowing that n should be 7. To derive it in an Olympiad is close to impossible fo...
by jaap
Mon Jul 09, 2018 3:21 pm
Forum: Number
Topic: an old maths olympiad question
Replies: 27
Views: 2632

Re: an old maths olympiad question

So people here can't solve an Olympiad question I probably could but I can't be bothered. Spending a couple of minutes here and there during breaks at work is rather different from actually solving it in Olympiad. Olympiad questions are often hard until some specific insight hits you, and it can ta...
by jaap
Mon Jul 09, 2018 12:28 pm
Forum: Number
Topic: an old maths olympiad question
Replies: 27
Views: 2632

Re: an old maths olympiad question

I can derive a cubic equation that cos(x) must satisfy where x is half the central angle, i.e. x=180/n. It is straightforward to see that: A1A2 = 2sin(x) A1A3 = 2sin(2x) A1A4 = 2sin(3x) Substituting this in the equation, and using the angle sum formulae sin(a+b)=sin(a)cos(b)+sin(b)cos(a) and cos(2a)...
by jaap
Mon Jul 09, 2018 9:02 am
Forum: Number
Topic: an old maths olympiad question
Replies: 27
Views: 2632

Re: an old maths olympiad question

Far as I know, a "regular" polygon has sides of equal length, call it length S, so: 1/A1A2 = 1/A1A3 + 1/A1A4 is the same as 1/S^2 = 1/S^2 + 1/S^2, the same as 1 = 1 + 1 so No polygon satisfies... I could be missing something but did you say there were 10 questions? A 1 , A 2 , A 3 , A 4 are consecu...
by jaap
Sun Jul 08, 2018 6:27 am
Forum: Number
Topic: an old maths olympiad question
Replies: 27
Views: 2632

Re: an old maths olympiad question

Whatever the missing question is, its answer probably relies on the fact that that polynomial can be written as (n-2)(n-1)n(n+1)(n+2)(n+3)+3. I have updated ot now. Is it my inexperience that I cannot see how to factor the polynomial? No. I cheated and typed it into Wolfram Alpha. If I were in a co...
by jaap
Sat Jul 07, 2018 2:58 pm
Forum: Number
Topic: an old maths olympiad question
Replies: 27
Views: 2632

Re: an old maths olympiad question

S_r wrote:
Sat Jul 07, 2018 3:38 am
The question:
Prove that for no integer n, n6+3n5-5n4-15n3+4n2+12n+3
Whatever the missing question is, its answer probably relies on the fact that that polynomial can be written as
(n-2)(n-1)n(n+1)(n+2)(n+3)+3.