attempt to solve pythagorean triplets.

1 files changed, 57 insertions, 0 deletions

diff --git a/spec/euler/problem_nine_spec.rb b/spec/euler/problem_nine_spec.rb
new file mode 100644
index 0000000..3ec4f76
--- /dev/null
+++ b/spec/euler/problem_nine_spec.rb
@@ -0,0 +1,57 @@
+require "spec_helper"
+
+describe "problem nine" do
+  # A Pythagorean triplet is a set of three natural numbers, a < b < c, for which, a^2 + b^2 = c^2
+  # For example, 3^2 + 4^2 = 9 + 16 = 25 = 5^2.
+
+  # There exists exactly one Pythagorean triplet for which a + b + c = 1000.
+  # Find the product abc.
+  #
+  class PythagoreanTriplet
+    include Enumerable
+
+    def initialize(max = 100_000)
+      @max = max
+    end
+
+    def each(&block)
+      triplets.each(&block)
+    end
+
+    private
+
+    def triplets
+      Enumerator.new do |yielder|
+        0.upto(@max) do |n|
+          x = n * n
+          y = (n+1) * (n+1)
+          z = (n+2) * (n+2)
+          if x + y == z
+            puts "#{n}: MATCH"
+            yielder.yield([n, n+1, n+2]) 
+          else
+            puts "#{n}: no match"
+          end
+        end
+      end
+    end
+  end
+
+  subject { PythagoreanTriplet.new }
+
+  it "returns the triplet for 25" do
+    expect(subject.first).to eql([3, 4, 5])
+
+    result = subject.find do |triplet|
+      (triplet.last * triplet.last) == 25
+    end
+    expect(result).to eql([3, 4, 5])
+  end
+
+  it "returns the triplet for 1000" do
+    result = subject.find do |triplet|
+      (triplet.last * triplet.last) == 1_000
+    end
+    expect(result).to eql(10)
+  end
+end