Search found 51 matches

by DJohn
Mon Sep 23, 2019 4:06 pm
Forum: Clarifications on Project Euler Problems
Topic: Problem 680
Replies: 1
Views: 12

Re: Problem 680

The question says that for some K iterations, one array value needs to be swapped with another array value in A. That is not what the question says. the $j$-th operation consists of reversing the order of those elements in $A$ with indices between $s_j$ and $t_j$ So if the array is 0, 1, 2, 3, 4, 5...
by DJohn
Mon Sep 09, 2019 3:49 pm
Forum: Clarifications on Project Euler Problems
Topic: Problem 503
Replies: 10
Views: 2085

Re: Problem 503

A strategy is just a function from "what has happened so far" to "what to do next". There are only n cards and games can't go on forever, so there's a finite number of possibilities for "what has happened so far" and a finite number of possible strategies. For small n it's possible to test all of th...
by DJohn
Tue Aug 06, 2019 8:43 am
Forum: Clarifications on Project Euler Problems
Topic: Problem 137
Replies: 10
Views: 2745

Re: Problem 137

RishadanPort wrote:
Mon Aug 05, 2019 10:22 pm
IE x = -2 and x = 1/2 both result in Af(x) = 2
$A_F(-2) \neq 2$. It doesn't converge.
by DJohn
Tue Jul 30, 2019 8:48 am
Forum: Clarifications on Project Euler Problems
Topic: Problem 111
Replies: 28
Views: 5473

Re: Problem 111

RishadanPort wrote:
Tue Jul 30, 2019 4:08 am
I am assuming the same prime can be in 2 or more categories, and have it's sum added in multiple times?
It doesn't happen in the case of 4 digit primes, but there's nothing in the problem statement that rules it out. Each S() is evaluated independently.
by DJohn
Mon Jul 29, 2019 12:31 pm
Forum: Clarifications on Project Euler Problems
Topic: Problem 111
Replies: 28
Views: 5473

Re: Problem 111

I might be missing something... But why doesn't the question just ask: "What is the sum of all 10 digit primes"... end of question. Simply because the solution is not the sum of all 10 digit primes. For 4 digit numbers, 1013 is prime, but we don't include it in S(4, 1) because it only has 2 1s and ...
by DJohn
Fri Jun 14, 2019 4:09 pm
Forum: News, Suggestions, and FAQ
Topic: Errors/Warnings/Bugs
Replies: 513
Views: 98906

Re: Errors/Warnings/Bugs

Problem 411 is missing its picture.
by DJohn
Wed May 08, 2019 10:30 am
Forum: Clarifications on Project Euler Problems
Topic: Problem 177
Replies: 24
Views: 11564

Re: Problem 177

I'm wondering if the tolerance could be wrong for the way I'm calculating this problem. Is it possible that, given my calculation method / choice of language, the tolerance should actually be 10^(-8) or 10^(-10) or something? For the method that I used, at least, it's quite tolerant of varying tole...
by DJohn
Fri Apr 05, 2019 3:06 pm
Forum: Clarifications on Project Euler Problems
Topic: Problem 663
Replies: 11
Views: 2160

Re: Problem 663

Just wanted to check, say the array $A_n = [8, -1, 2, 3, -5, 6, -100, 2, 4, 6]$, so would the maximum sub-array sum be $8 + (- 1) + 2 + 3 + (- 5) + 6 = 13$. So if negative values can be "absorbed", we should "absorb" them? That's what the definition of M implies, and you won't get the right value f...
by DJohn
Tue Jan 22, 2019 2:15 pm
Forum: Clarifications on Project Euler Problems
Topic: Problem 175
Replies: 4
Views: 1908

Re: Problem 175

While investigating problem 175 I calculated that f(242)=13 and f(241) = 17, using the function developed for problem 169. However the problem statement for 175 states that f(241) = 13 and f(240) =17. Which of us is right? The problem statement is correct. It's possible that your implementation for...
by DJohn
Thu Sep 27, 2018 9:52 am
Forum: Clarifications on Project Euler Problems
Topic: Problem 637
Replies: 3
Views: 995

Re: Problem 637

I don't understand where you think the problem is. No one has made any claims about f(10211914,10), and the problem statement does not give any algorithm. With 1. 1+0+2+1+1+91+4 = 100 => 2. 1+0+0 = 1 you've shown that f(10211914,10) <= 2. But then where do you get 10211914 -9*floor(10211914/9) = 1 T...
by DJohn
Mon Sep 17, 2018 9:44 am
Forum: Recreational
Topic: Suggest me a book
Replies: 13
Views: 9184

Re: Suggest me a book

Albert H Beiler "Recreations in the Theory of Numbers" is an interesting one. It belongs to the very end of the hand-computation era, just as computers were starting to take over. The methods he describes are very different to the ones you'd use now. That's what made it fascinating for me. It's a lo...
by DJohn
Fri Aug 31, 2018 9:21 am
Forum: Clarifications on Project Euler Problems
Topic: Problem 504
Replies: 12
Views: 3898

Re: Problem 504

Yes. A point is not strictly inside if it's on an edge.
by DJohn
Fri Jun 22, 2018 9:39 am
Forum: Clarifications on Project Euler Problems
Topic: Problem 004
Replies: 83
Views: 13858

Re: Problem 004

Please don't post code or solutions (even wrong ones): see the big red text at the top. Are you certain that your palindrome() function works? Try testing it with a few numbers that you know are palindromes, and some that you know aren't. There is definitely more than one palindromic product of two ...
by DJohn
Thu May 10, 2018 3:10 pm
Forum: Clarifications on Project Euler Problems
Topic: problem 206
Replies: 33
Views: 10270

Re: problem 206

You don't need a calculator to see that you've gone wrong: The last digit of 1388659302 is 2. Whatever the square is, its last digit will be 4, not 0.
by DJohn
Wed May 02, 2018 11:08 am
Forum: Combinatorics
Topic: Container Packing Problem
Replies: 5
Views: 5289

Re: Container Packing Problem

This is a simpler version of Problem 324 https://projecteuler.net/problem=324
by DJohn
Thu Sep 28, 2017 10:06 am
Forum: Clarifications on Project Euler Problems
Topic: Problem 610
Replies: 16
Views: 4281

Re: Problem 610

RobertStanforth wrote:
Wed Sep 27, 2017 6:12 pm
'CM' is indeed considered a lower denomination than 'M'
That's what I was missing. I wasn't clear what a 'denomination' was.
by DJohn
Wed Sep 27, 2017 11:05 am
Forum: Clarifications on Project Euler Problems
Topic: Problem 610
Replies: 16
Views: 4281

Re: Problem 610

To write a roman numeral you do so by using 'greedy' algorithm. The trouble is, neither the problem nor "About... Roman Numerals" mention a greedy algorithm. I agree that CMD is not a minimal representation of 1400 (I'd say it wasn't a valid representation at all), but that comes from external expe...
by DJohn
Fri Sep 15, 2017 10:39 am
Forum: Recreational
Topic: How to factor
Replies: 8
Views: 6629

Re: How to factor

It depends on how big the numbers are. For small numbers, my PE library has code to generate a table of the smallest prime divisor for all numbers up to some limit (it's not hard to adapt the usual sieve to generate this). That lets you produce a complete prime factorisation very quickly: keep divid...
by DJohn
Thu Aug 03, 2017 10:43 am
Forum: Clarifications on Project Euler Problems
Topic: Problem 317
Replies: 38
Views: 11294

Re: Problem 317

Therefore, the value of $\pi$ must be stated in the problem description the same way it stated for $g$. The problem is asking for the value you'd get by calculating the volume exactly, then rounding it to four decimal places. It doesn't mention $\pi$ at all. Any method of finding that rounded value...
by DJohn
Mon Jul 10, 2017 10:18 am
Forum: News, Suggestions, and FAQ
Topic: Difficulty Ratings
Replies: 28
Views: 8802

Re: Difficulty Ratings

(It could just be my lack of background in some of the subjects on which these problems are based.) I'm pretty sure that's exactly what it is. It's impossible to produce an absolute objective difficulty rating, because every person is coming to Project Euler with a different set of skills. I'm weak...