Data commit

Task/Generator-Exponential/Ruby/generator-exponential-1.rb

@@ -0,0 +1,20 @@
+# This solution cheats and uses only one generator!
+
+def powers(m)
+  return enum_for(__method__, m) unless block_given?
+  0.step{|n| yield n**m}
+end
+
+def squares_without_cubes
+  return enum_for(__method__) unless block_given?
+
+  cubes = powers(3)
+  c = cubes.next
+  powers(2) do |s|
+    c = cubes.next while c < s
+    yield s unless c == s
+  end
+end
+
+p squares_without_cubes.take(30).drop(20)
+# p squares_without_cubes.lazy.drop(20).first(10)   # Ruby 2.0+

Task/Generator-Exponential/Ruby/generator-exponential-2.rb

@@ -0,0 +1,23 @@
+# This solution uses three generators.
+
+def powers(m)
+  return enum_for(__method__, m) unless block_given?
+  0.step{|n| yield n**m}
+end
+
+def squares_without_cubes
+  return enum_for(__method__) unless block_given?
+
+  cubes = powers(3) #no block, so this is the first generator
+  c = cubes.next
+  squares = powers(2) # second generator
+  loop do
+    s = squares.next
+    c = cubes.next while c < s
+    yield s unless c == s
+  end
+end
+
+answer = squares_without_cubes # third generator
+20.times { answer.next }
+p 10.times.map { answer.next }

Task/Generator-Exponential/Ruby/generator-exponential-3.rb

@@ -0,0 +1,14 @@
+def filtered(s1, s2)
+  return enum_for(__method__, s1, s2) unless block_given?
+  v, f = s1.next, s2.next
+  loop do
+    v > f and f = s2.next and next
+    v < f and yield v
+    v = s1.next
+  end
+end
+
+squares, cubes = powers(2), powers(3)
+f = filtered(squares, cubes)
+p f.take(30).last(10)
+# p f.lazy.drop(20).first(10)   # Ruby 2.0+