Problem 524

A place to air possible concerns or difficulties in understanding ProjectEuler problems. This forum is not meant to publish solutions. This forum is NOT meant to discuss solution methods or giving hints how a problem can be solved.
Forum rules
As your posts will be visible to the general public you
are requested to be thoughtful in not posting anything
that might explicitly give away how to solve a particular problem.

This forum is NOT meant to discuss solution methods for a problem.

In particular don't post any code fragments or results.

Don't start begging others to give partial answers to problems

Don't ask for hints how to solve a problem

Don't start a new topic for a problem if there already exists one


See also the topics:
Don't post any spoilers
Comments, questions and clarifications about PE problems.
Post Reply
phsr
Posts: 27
Joined: Tue Dec 15, 2009 12:00 am

Problem 524

Post by phsr »

Maybe this is obvious, but does 'lexicographic order' include delimiters?

Does {102,41...} sort before or after {1024,2...}?
TripleM
Posts: 382
Joined: Fri Sep 12, 2008 3:31 am

Re: Problem 524

Post by TripleM »

No. You're ordering the permutations as lists, not as alphanumeric strings.
phsr
Posts: 27
Joined: Tue Dec 15, 2009 12:00 am

Re: Problem 524

Post by phsr »

Just to be absolutely clear: the lexicographic order for the numbers from 1 to 20 is

1,10,11,12,13,14,15,16,17,18,19,2,20,3,4,5,6,7,8,9. Do we agree??
User avatar
jaap
Posts: 554
Joined: Tue Mar 25, 2008 3:57 pm
Contact:

Re: Problem 524

Post by jaap »

phsr wrote:Just to be absolutely clear: the lexicographic order for the numbers from 1 to 20 is

1,10,11,12,13,14,15,16,17,18,19,2,20,3,4,5,6,7,8,9. Do we agree??
No.
Think of each number in a list as a single letter in a word.
(2,3,4)<(10,1,1)<(10,1,2)<(10,4,1)<(11,3,3)<(104,1,2)<(1030,0,0)

Each 'coordinate' is sorted numerically, and lexicographic refers to how you deal with more than one coordinate - left to right, until the first coordinate where there is a difference, just like the letters of a word when sorting alphabetically.

https://en.wikipedia.org/wiki/Lexicographical_order
mattmadi
Posts: 2
Joined: Sat Oct 10, 2015 4:15 am

Re: Problem 524

Post by mattmadi »

Do people think that this problem is solvable with just pencil and paper?

I thought I had found a pencil and paper solution, but it's wrong.
:(

*EDIT*: Not just pencil and paper. I need some computing power to deal with quite large numbers.

*EDIT* SOLVED with pencil and paper and calculator.
Post Reply