Created
February 9, 2016 09:29
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require 'active_support/core_ext/enumerable' | |
require 'pry' | |
class ProjectEuler | |
attr_accessor :hash, :array | |
def initialize( args = {} ) | |
self.hash = {} | |
self.array = [] | |
end | |
def three_and_five | |
# If we list all the natural numbers below 10 that are multiples of 3 or 5, we get 3, 5, 6 and 9. The sum of these multiples is 23. | |
# Find the sum of all the multiples of 3 or 5 below 1000. | |
( 1..999 ).each do |n| | |
next unless n % 3 == 0 || n % 5 == 0 | |
array.push n | |
end | |
array.sum | |
end | |
def even_fibonacci_numbers | |
# Each new term in the Fibonacci sequence is generated by adding the previous two terms. By starting with 1 and 2, the first 10 terms will be: | |
# 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, ... | |
# By considering the terms in the Fibonacci sequence whose values do not exceed four million, find the sum of the even-valued terms. | |
array = [ 1, 2 ] | |
past = 1 | |
present = 2 | |
loop_through = true | |
while loop_through do | |
array.push( past + present ) | |
past = present | |
present = array.last | |
loop_through = false if ( past + present ) > 4000000 | |
end | |
array.select{ |n| n % 2 == 0 }.sum | |
end | |
def largest_prime_factor | |
# The prime factors of 13195 are 5, 7, 13 and 29. | |
# What is the largest prime factor of the number 600851475143 ? | |
check_again = lambda{ |n| } | |
number = 600851475143 | |
hash = { | |
number => { } | |
} | |
(2..( number / 2 ) ).each do |n| | |
hash[ number ][ number / n ] = {} if number % n == 0 | |
end | |
end | |
end |
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