I had an easy time with this one, which makes me feel a lot better about all the ones I had problems with!
No fancy-pants recursion or math short-cuts here, just a straight forward logic problem. The only “trick” here is to realize that since a <e; b < c, we only need to check values of a and b up to 499.
I’m sure you could whittle that number down by crunching the numbers, but it’s good enough for me!
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I listen to a lot of music at work. All day, every day.
It helps smooth frustrations, keeps me awake, and provides “color” for my day. I want my office to feel like a 1960’s Sci-Fi movie!
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40 problems down, 10 more till level 2!
The real trick here is to cut down on the numbers you check. Since the problem gives you 918273645 as an example we know the answer must be greater than or equal to it…meaning we only need to check digits that start with 9!
I don’t actually do it because I couldn’t figure out an elegant way to do, but it runs in just a few milliseconds so it’s fast enough in my book.
Another important factor to note is that you only need to check numbers up to 9_876 since this is the first ‘half’ of the largest pandigital possible.
Those two tricks will cut down the calculations you need to run to just a few thousand.
What is the largest 1 to 9 pandigital 9-digit number that can be formed as the concatenated product of an integer with (1,2, … , n) where n 1?
def get_pandigital? n
nums = []
(1..9).each do |digit|
nums += (n * digit).to_s.split ''
return 0 if nums.size != nums.uniq.size || nums.include?('0')
return nums.join('').to_i if nums.size == 9
end
end
solution = 0
(9..9_876).each do |n|
# could do better by only looking at 9's!
result = get_pandigital? n
if result > solution
solution = result
end
end
puts solution
Check out all of my solutions on bitbucket!
It’s been a while since I’ve done one of these, so I was afraid of being rusty but it worked out alright. I used the generator I made a while back to create the primes (pre-filled to the example given in the project) and used procs to take care of the truncation.
BAM!
The number 3797 has an interesting property. Being prime itself, it is possible to continuously remove digits from left to right, and remain prime at each stage: 3797, 797, 97, and 7. Similarly we can work from right to left: 3797, 379, 37, and 3.
Find the sum of the only eleven primes that are both truncatable from left to right and right to left.
load 'prime_generator.rb'
def prime? n, truncate
return false if !$primer.is_prime?(n)
return true if n < 10
prime? truncate.call(n), truncate
end
left = Proc.new { |n| n / 10 }
right = Proc.new { |n| n % 10**Math.log10(n).to_i }
$primer = Prime_Generator.new 3_797
n, sum, found = 0, 0, 0
while found < 11 do
if (n += 1) > 10 && prime?(n, left) && prime?(n, right)
found += 1
sum += n
end
end
puts sum
Also, I’ve finally moved my project euler solutions over to bitbucket. Long live Mercurial!
I don’t normally like to blog links, Twitter and Google Reader are much better platforms for that, however this was so cool I just had to shout it out.
Read more about it, and check it out yourself: Otomato
The rules for the automation are simple, but the hypnotic patterns that emerge are truly beautiful and interesting. The user interface is both easy and fun to use, and it does a great job of showing the simple beauty of what you’re listening to.
The music reminds me a lot of one of my favorite bands Boards of Canada, so if like the sound of this then check them out, it makes for great programming music.
In the last two weeks I’ve had the great fortune to attend two fantastic conferences here in Orlando.
Both completely free events, and both were fun, inspiring, and eye-opening in their own ways. I came away feeling inspired, invigorated, and with a couple of new nerdy (read: cool) t-shirts!
Orlando CodeCamp was incredibly educational and informative with it’s tech-heavy, hour-long formal presentations. I can’t imagine all the hard work put in by the speakers and volunteers to have such a large and superior quality event run, and run so smoothly.
There was a definite collegial vibe (taking place at the beautiful Seminole County College campus didn’t hurt!) but oh how I wish my university experience was as interesting, efficient, relevant, and productive.
Special thanks to the ONETUG president Esteban Garcia for patiently and thoroughly answering all my inane TFS questions. I’ve avoided TFS talks in the past because I thought they would be boring, but boy was I wrong! It really cool to see everything up and integrated like that!
Also another special thanks to SubMain for the CodeIt.Right licensce I won. I’m already putting it to good use!
If CodeCamp felt like school, then BarCamp felt more like…Woodstock. The event took place in the Wall Street Plaza, with talks taking place in local venues like One-Eyed Jacks, Slingapours, and The Gibson Showroom. The presentation times and topics were updated throughout the day on a giant white board, and there was a great little mobile site for keeping track of the ever evolving schedule the on your iPhone. (I’m an Android fanboy, but I don’t think I’ve ever seen so many Apple products in one place before!)
The talks ranged from the technical to the artistic to the entrepreneurial, and there were strong revolutionary, community and outside-the-box undercurrents behind most talks.
The session that most picqued my interest was done by Stan Schultes, Microsoft MVP and organizer of the BarCamp Sarasota. He led a ‘birds of a feather’ style centered around software start-ups, and what cities like San Francisco, Boston and New York have that we in the “Greater Central Florida Region” don’t….and how we can organize to fix it!
The biggest take-away for me however is getting to see and meet so many inspired and passionate makers, shakers and enthusiasts out there trying to make a difference.
Photo Credit: Nick Pettit
I’m looking forward to checking out recently discovered entities like Orlando Coding Dojo, Urban ReThink, and Familab events in the near future.
Big shout out to ONETUG, ORUG, and Envy Labs for being such big drivers behind these events and a big thanks to all the organizers, sponsors and community. Fantastic job!
Oh, and I almost forgot to mention the best part about these two events: They’re recurring!
I’m looking forward to seeing you all again soon!
Just read an excellent blog post: How to Steal Like An Artist. I really liked the writing style and the message so I took a look around the site.
Great stuff!
I particularly liked the fun and cynicism of this one:
Overheard on the Titanic by Austin Kleon
There are more blog posts and artwork at the authors site: http://www.austinkleon.com/.
Thanks phntm42!
I like unsigned integers, always have. It’s more correct, concise and expressive, you get more (positive) space out of it and you’re preventing bugs by design. What’s not to love?
Well…
I’ve been nooking CLR via C# and it’s a fantastic read for anyone who wants to ‘get serious’ about .Net. The book’s so crammed full of good information it’s hard not to gush, but I digress.
I was nooking, you see, and I came across this recommendation:
“Use signed data types (such as Int32 and Int64 instead of unsigned numeric types such as UInt32 and UInt64) wherever possible.”
Jeffrey Richter continues:
“This allows the compiler to detect more overflow/underflow errors. In addition, various parts of the class library (such as Array’s and String’s Length properties) are hard-coded to return signed values, and less casting is required as you move these values around in your code.”
Casting is ugly, no argument there but I don’t care much about the overflow/underflow errors. I generally don’t enable overflow checking, there’s no political statement here, it’s just never come up.
And it still feels wrong for me to declare a value signed when I know that it shouldn’t be.
(Richter recommends enabling checking for debug builds, and disabling for release. Sound advice!)
But here’s real the kicker for me:
In addition, unsigned numeric types are not CLS-compliant.
Doh. I did a bit of searching to try and track down why it’s not part of the CLS, and I found that Brad Abrams expresses it best in this post:
“The general feeling among many of us is that the vast majority of programming is done with signed types. Whenever you switch to unsigned types you force a mental model switch (and an ugly cast). In the worst cast you build up a whole parallel world of APIs that take unsigned types. The value of avoiding the ‘< 0' check is not worth the inclusion of generics in the CLS"
Alright, I give in. I’m apparently in the minority, these guys are way smarter than I am, and it is easier, if not more concise. So it goes.
Goodbye for now uint, you’ll always hold a positive place in my heart.
Just like Weezer:
He doesn't look evil, does he?
It's alive!
I’ve finally gotten around to messing with Arduino, and it’s been a lot of fun! I picked up an “Experimentation Kit” from Adafruit and it contained everything I needed to get started, including a little booklet of circuit examples.
I don’t know that I’ve gained any programming insight from my experimentations, but I’d wager most developers would enjoy this sort of thing. It could make an excellent Christmas gift for that hard-to-buy-for geek in your family!