Why do I publish my solutions ?
Almost always the solutions for problems at Project Euler consist of two parts:
- finding a mathematical way to break down the problem into its elements
- writing an efficient program for step 1
There are already several blogs or code repositories (vast majority hosted at GitHub) where you
can find solutions to the Project Euler problems.
I strive to:
- explain my choice of algorithms and data structures
- write fully commented C++ source code that compiles without warnings and without any external libraries
- offer interactive tests for most problems
- link to relevant Wikipedia / MathWorld / OEIS pages
- link to other solutions, especially those that are written in other programming languages
Let's not forget that this website helps me, too: only if I can explain a solution to someone else then I can be sure that I truly understood it in the first place.
And practicing some of the lesser used features of C++ (such as algorithm hidden inside STL, like
std::next_permutation) improves my overall coding skills as well.
Sounds like a win-win situation ... ☺
"The Solutions On This Website Are Too Complicated ..."
"... someone else wrote much shorter/simpler programs !".
Yes, several solutions to the original Project Euler problems are indeed much more straightforward.
But they usually:
- don't scale well (see notes about Hackerrank)
- have about the same number of lines of code, but no comments
- use language-specific features, such as Python's BigNum support
The commercial website HackerRank offers an online programming environment. They have a huge variety of coding exercises and competitions for beginners and "masters", too.
Some Project Euler problems are modified by HackerRank and in most cases they become (much) harder.
There is a strict time limit - often 2 seconds for C++ code - whereas Project Euler just recommends that your program should finish in less than 1 minute.
The majority of my programs have a perfect 100% score at HackerRank, unless indicated otherwise.
The input format of my interactive tests is usually identical to HackerRank's.
If HackerRank's modifications substantially change my algorithm then I need to insert
ORIGINAL refers to the original Project Euler problem and
#ifndef ORIGINAL (or just
contains HackerRank specific code.
Note: the test cases at Hackerrank "discovered" a few bugs in my code. Even though I had the correct result for Project Euler,
some of my programs failed to pass all Hackerrank tests.
@Hackerrank: Thanks for including those nasty edge cases most of us forget about !
I created this feature because I often had trouble in finding some hidden bugs in my code:
I had the right algorithm, hopefully the best data structure and somehow my results were incorrect.
If you use my interactive tests then you can hopefully find your bugs, too.
Please note that I set a execution timeout of 1 second on my server. Memory is typically limited to 64 MByte.
If too many users are running tests, then some processes might get killed in order to keep the server responsive.
In addition, some input/output values are forbidden - especially the default input from the original Project Euler problem.
green problems solve the original Project Euler problem and have a perfect score of 100% at Hackerrank, too.
yellow problems score less than 100% at Hackerrank (but still solve the original problem).
gray problems are already solved but I haven't published my solution yet.
blue problems are already solved and there wasn't a Hackerrank version of it (at the time I solved it) or I didn't care about it because it differed too much.
Please click on a problem's number to open my solution to that problem: