elreimundo’s gists

elreimundo / sumofprimes.rb

Last active December 20, 2015 00:59

Here's a pretty simple prime number generator I used for a problem in ProjectEuler (specifically, calculate the sum of every prime below 2,000,000, although this can be generalized to sum every prime below any integer)

	def sumofprimesbelow number
	prime_array = [3,5]
	current_num = 7
	while current_num < number
	prime_array.each do \|factor\|
	if current_num % factor == 0
	break
	elsif factor > Math.sqrt(current_num)
	prime_array << current_num
	break

elreimundo / countofmultiples.rb

Created July 17, 2013 15:19

Project Euler problem #1 : "Find the sum of all of the whole numbers less than 1000 that are multiples of either 3 or 5." I thought that problem was too quick, so I generalized it to "Find the sum of all of the whole numbers less than n that are multiples of either x or z," then ran n=1000,x=3,z=5.

	def countofmultiples (num,firstfactor,secondfactor)
	count = 0
	1.upto(num-1) do \|check\|
	if check % firstfactor == 0 \|\| check % secondfactor == 0
	count += check
	end
	end

	count
	end

elreimundo / fiftysixpuzzle.rb

Created July 17, 2013 15:08

A friend posted a math puzzle: "Find the smallest integer that ends in 56, is divisible by 56, and whose digits add to 56." Here's the Ruby script I wrote to solve the puzzle.

	def digitsum num
	currentsum = 0
	(Math.log(num,10).ceil).downto(0) do \|digit\|
	currentsum = currentsum + num/(10**digit)
	num = num%(10**digit)
	end

	currentsum
	end

elreimundo / englishnumber.rb

Created July 17, 2013 15:04

Not sure how elegant this is, but here is my number-to-its-English-word-counterpart translator

	def numwords any_number
	bignumwords any_number, []
	end

	def bignumwords number, big_array
	place_names = {1 => 'thousand',
	2 => 'million',
	3 => 'billion',
	4 => 'trillion'}
	comma_count = Math.log(number,10).floor / 3

elreimundo / times_table

Last active December 19, 2015 14:09

So I thought this would show a (not-very-well-spaced) times table with individual values separated by a space and each row on a new line. What am I missing?

	def times_table(rows)
	bigarray = []
	1.upto(rows) do \|x\|
	newarrayrow=[]
	1.upto(rows) do \|y\|
	newarrayrow << x*y
	end
	bigarray << newarrayrow.join(' ')
	end

elreimundo / triangle_validity

Last active December 19, 2015 13:18

Am I cheating? When I taught Geometry, I used to teach my kids that this was the only requirement for a (planar) triangle. I feel like I should be teaching the machine to check for isosceles, equilateral, etc., but if all we want is to determine if a triangle is valid...

	def valid_triangle?(a, b, c)
	(a + b > c) && (a + c > b) && (b + c > a)
	end