Blogs

Find the difference between the sum of the squares of the first one hundred natural numbers and the square of the sum. ---- We don't actually need a computer to solve this problem, but why not?   The formula for the sum of the squares of the first n natural numbers is:  n*(n+1)*(2n+1)/6...

What is the smallest number that is evenly divisible by all of the numbers from 1 to 20? ---- To solve this problem easily, we need to remember that the smallest number that is evenly divisible by two numbers is their least common multiple. Armed with this knowledge (and the fact that ruby already has...

Find the largest palindrome made from the product of two 3-digit numbers. ----- First, I defined a palindrome recursively: a number is one if its first and last digits are the same, and if the inside is also a palindrome. def palindrome?(digitArr) if digitArr.empty? true elsif digitArr.length == 1 true...

What is the largest prime factor of the number 600851475143 ? ----- I wrote this piece of disgusting, un-Rubylike Ruby to get the answer by creating a list of a number's prime factors: def factor(composite) i=1 flag=false primefactors =[] while (i < composite) i=i+1 primefactors.each{|p| flag...

I was first introduced to the term polyglot when I was in high school. Our French class did a presentation at a Foreign Language Day. I have this vague recollection that the theme of the day was "Polyglots Have More Fun". I've always liked the word, so I was thrilled to see Neal Ford using...

The problem: Find the sum of all the even-valued terms in the [Fibonacci] sequence which do not exceed four million. Here's my fibonacci function: def fib(limit =nil) f1 = 0 f2 = 1 while (not limit or f2 <= limit) yield f2 f1,f2 = f2, f1+f2 end end And here's how I use it to get the answer...

I'm taking Bill Wagner up on his Project Euler challenge , but in Ruby. I've secretly wanted to learn Ruby for a long time, and this looks like the perfect chance. So if my code makes your eyes bleed, it's cause I'm a total n00b. Without further ado (because the excitement was becoming...