tidying up more solutions

euler.rb

@@ -1,8 +1,19 @@
 require 'prime'
 
 class Integer
-  def to_digit_list
+  def choose(k)
-    self.to_s.split('').map(&:to_i)
+    factorial / (k.factorial * (self - k).factorial)
+  end
+
+  def divisors
+    divisors = []
+    (1..Math.sqrt(self).to_i).each do |num|
+      if self % num == 0
+        divisors << num
+        divisors << self / num
+      end
+    end
+    divisors
   end
 
   def factorial
@@ -15,8 +26,8 @@ class Integer
     i
   end
 
-  def choose(k)
+  def to_digit_list
-    factorial / (k.factorial * (self - k).factorial)
+    self.to_s.split('').map(&:to_i)
   end
 end
 

euler012.rb

@@ -1,17 +1,7 @@
-class Integer
+require_relative 'euler'
-  def divisors
-    divisors = []
-    (1..Math.sqrt(self).to_i).each do |num|
-      if self % num == 0
-        divisors << num
-        divisors << self / num
-      end
-    end
-    divisors
-  end
-end
 
-triangle = Enumerator.new do |y|
+def triangle_enumerator
+  Enumerator.new do |y|
     sum = 1
     next_num = 2
     loop do
@@ -20,11 +10,8 @@ triangle = Enumerator.new do |y|
       next_num += 1
     end
   end
-
-val = triangle.next
-
-while val.divisors.count < 500
-  val = triangle.next
 end
 
-puts val
+def solution
+  triangle_enumerator.take_while { |x| x.divisors.count <= 500 }.last
+end

euler013.rb

@@ -1,4 +1,5 @@
-puts (37107287533902102798797998220837590246510135740250 +
+def solution
+  (37107287533902102798797998220837590246510135740250 +
   46376937677490009712648124896970078050417018260538 +
   74324986199524741059474233309513058123726617309629 +
   91942213363574161572522430563301811072406154908250 +
@@ -98,3 +99,4 @@ puts (37107287533902102798797998220837590246510135740250 +
   72107838435069186155435662884062257473692284509516 +
   20849603980134001723930671666823555245252804609722 +
   53503534226472524250874054075591789781264330331690).to_s[0..9]
+end

euler014.rb

@@ -1,23 +1,16 @@
 def collatz(num)
-  list = []
+  [].tap do |list|
-  current_num = num
+    until num == 1
-  while current_num > 1
+      if num.even?
-    list << current_num
+        list << (num = num / 2)
-    if current_num % 2 == 0
-      current_num /= 2
       else
-      current_num = 3*current_num + 1
+        list << (num = (3 * num) + 1)
       end
     end
     list << 1
   end
-
-def longest_chain(num)
-  chain_length = {}
-  (1..num).each do |starting_num|
-    chain_length[starting_num] = collatz(starting_num).count
-  end
-  chain_length.sort_by { |key, value| value }.last
 end
 
-puts longest_chain(999999)
+def solution
+  (1..999999).map { |i| collatz(i).count }.each_with_index.max[1] + 1
+end

euler015.rb

@@ -1,16 +1,9 @@
-def factorial(n)
+require_relative 'euler'
-  i = 1
-  while (n > 0)
-    i *= n
-    n -= 1
-  end
-  i
-end
-
-def combination(n, k)
-  factorial(n) / (factorial(k) * factorial(n-k))
-end
 
 def lattice_paths(size)
-  combination(2*size, size)
+  (2*size).choose(size)
+end
+
+def solution
+  lattice_paths(20)
 end