Euler Project in Ruby - Problem 5

euler5.rb

upto = 20
 
def prime? x
  (2..x-1).each { |y| return false if x % y == 0 }
  true
end
 
# For speed reasons we want to find max possible increment
def increment upto
  a = 1
  (1..upto).each { |x| a*= x if prime? x }
  a
end
 
def no_remainder? x, upto       
  (1..upto).each { |y| return false if x % y != 0 }
  true
end
 
increment = increment upto
x = increment
try_number = 1
 
while true
  if no_remainder? x, upto
    puts "The smallest number is #{x}"
    break
  end
  try_number += 1
  x = try_number * increment 
end

Another clean and quick thing in Ruby.

def compute_lowest_dividing_number number
  for i in 2..(number/2)
    return i if number%i == 0
  end
  number
end

lcm = 1
n = 20
for i in 1..n
  # look ahead appraoch
  next_number = [i+1, n].min
  lcm *= compute_lowest_dividing_number(next_number) if lcm % next_number != 0
end
puts lcm