1 files changed, 41 insertions, 0 deletions
diff --git a/challenge-271/roger-bell-west/ruby/ch-2.rb b/challenge-271/roger-bell-west/ruby/ch-2.rb
new file mode 100755
index 0000000000..7a2ac232cd
--- /dev/null
+++ b/challenge-271/roger-bell-west/ruby/ch-2.rb
@@ -0,0 +1,41 @@
+#! /usr/bin/ruby
+
+require "set"
+
+def popcount(x0)
+  x = x0
+  c = 0
+  while x > 0 do
+    x &= x - 1
+    c += 1
+  end
+  return c
+end
+
+def sortbyonebits(a)
+  c = Hash.new
+  Set.new(a).each do |n|
+    c[n] = popcount(n)
+  end
+  return a.sort do |aa, bb|
+    if c[aa] == c[bb] then
+      aa <=> bb
+    else
+      c[aa] <=> c[bb]
+    end
+  end
+end
+
+require 'test/unit'
+
+class TestSortbyonebits < Test::Unit::TestCase
+
+  def test_ex1
+    assert_equal([0, 1, 2, 4, 8, 3, 5, 6, 7], sortbyonebits([0, 1, 2, 3, 4, 5, 6, 7, 8]))
+  end
+
+  def test_ex2
+    assert_equal([64, 128, 256, 512, 1024], sortbyonebits([1024, 512, 256, 128, 64]))
+  end
+
+end