Add property based tests for RedBlackTree (#8)

Fix quite some bugs in the implementation as well.
vorce · Oct 29, 2018 · 2e06869 · 2e06869
1 parent 2f8df28
commit 2e06869
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diff --git a/lib/red_black_tree.ex b/lib/red_black_tree.ex
@@ -8,6 +8,7 @@ defmodule Dasie.RedBlackTree do
 
   - http://www.cs.ox.ac.uk/ralf.hinze/WG2.8/32/slides/red-black-pearl.pdf
   - https://functional.works-hub.com/learn/Persistent-Red-Black-Trees-in-Haskell
+  - http://inst.eecs.berkeley.edu/~cs61b/fa17/materials/demos/ll-red-black-demo.html
   """
 
   defstruct data: nil,
@@ -142,22 +143,22 @@ defmodule Dasie.RedBlackTree do
     end
   end
 
-  def delete_left(element, %__MODULE__{color: :red} = node, compare_fn) do
-    %__MODULE__{node | left: do_delete(element, node.left, compare_fn)}
-  end
-
-  def delete_left(element, %__MODULE__{color: :black} = node, compare_fn) do
+  def delete_left(element, %__MODULE__{left: %__MODULE__{color: :black}} = node, compare_fn) do
     balance_left(%__MODULE__{node | left: do_delete(element, node.left, compare_fn)})
   end
 
-  def delete_right(element, %__MODULE__{color: :red} = node, compare_fn) do
-    %__MODULE__{node | right: do_delete(element, node.right, compare_fn)}
+  def delete_left(element, %__MODULE__{} = node, compare_fn) do
+    %__MODULE__{node | color: :red, left: do_delete(element, node.left, compare_fn)}
   end
 
-  def delete_right(element, %__MODULE__{color: :black} = node, compare_fn) do
+  def delete_right(element, %__MODULE__{right: %__MODULE__{color: :black}} = node, compare_fn) do
     balance_right(%__MODULE__{node | right: do_delete(element, node.right, compare_fn)})
   end
 
+  def delete_right(element, %__MODULE__{} = node, compare_fn) do
+    %__MODULE__{node | color: :red, right: do_delete(element, node.right, compare_fn)}
+  end
+
   def fuse(nil, right) do
     right
   end
@@ -188,20 +189,11 @@ defmodule Dasie.RedBlackTree do
             right: %__MODULE__{right | left: red.right}
         }
 
-      %__MODULE__{color: :black} = black ->
-        %__MODULE__{left | right: %__MODULE__{right | left: black}}
+      other ->
+        %__MODULE__{left | right: %__MODULE__{right | left: other}}
     end
   end
 
-  # This is probably the case i'm the least confident is doing the right thing
-  # at all times... maybe we can even get rid of it?
-  def fuse(
-        %__MODULE__{color: :black, right: nil} = left,
-        %__MODULE__{color: :black, left: nil} = right
-      ) do
-    balance_right(%__MODULE__{right | left: left})
-  end
-
   def fuse(
         %__MODULE__{color: :black} = left,
         %__MODULE__{color: :black} = right
@@ -216,35 +208,20 @@ defmodule Dasie.RedBlackTree do
             right: %__MODULE__{right | left: red.right}
         }
 
-      %__MODULE__{color: :black} = black ->
-        balance_left(%__MODULE__{left | right: %__MODULE__{right | left: black}})
+      other ->
+        balance_left(%__MODULE__{left | right: %__MODULE__{right | left: other}})
     end
   end
 
-  def balance_left(%__MODULE__{color: :black, left: %__MODULE__{color: :red} = x} = y) do
+  def balance_left(%__MODULE__{left: %__MODULE__{color: :red} = x} = y) do
     %__MODULE__{y | color: :red, left: %__MODULE__{x | color: :black}}
   end
 
-  def balance_left(
-        %__MODULE__{
-          color: :black,
-          right: %__MODULE__{color: :black} = z
-        } = y
-      ) do
-    balance(%__MODULE__{y | right: %__MODULE__{z | color: :red}})
+  def balance_left(%__MODULE__{right: %__MODULE__{color: :black} = z} = y) do
+    balance(%__MODULE__{y | color: :black, right: %__MODULE__{z | color: :red}})
   end
 
-  def balance_left(
-        %__MODULE__{
-          color: :black,
-          right:
-            %__MODULE__{
-              color: :red,
-              left: %__MODULE__{color: :black} = u,
-              right: %__MODULE__{color: :black}
-            } = z
-        } = y
-      ) do
+  def balance_left(%__MODULE__{right: %__MODULE__{color: :red, left: %__MODULE__{color: :black} = u} = z} = y) do
     %__MODULE__{
       u
       | color: :red,
@@ -259,32 +236,15 @@ defmodule Dasie.RedBlackTree do
     }
   end
 
-  def balance_left(node), do: node
-
-  def balance_right(%__MODULE__{color: :black, right: %__MODULE__{color: :red} = x} = y) do
+  def balance_right(%__MODULE__{right: %__MODULE__{color: :red} = x} = y) do
     %__MODULE__{y | color: :red, right: %__MODULE__{x | color: :black}}
   end
 
-  def balance_right(
-        %__MODULE__{
-          color: :black,
-          left: %__MODULE__{color: :black} = z
-        } = y
-      ) do
-    balance(%__MODULE__{y | left: %__MODULE__{z | color: :red}})
+  def balance_right(%__MODULE__{left: %__MODULE__{color: :black} = z} = y) do
+    balance(%__MODULE__{y | color: :black, left: %__MODULE__{z | color: :red}})
   end
 
-  def balance_right(
-        %__MODULE__{
-          color: :black,
-          left:
-            %__MODULE__{
-              color: :red,
-              left: %__MODULE__{color: :black},
-              right: %__MODULE__{color: :black} = u
-            } = z
-        } = y
-      ) do
+  def balance_right(%__MODULE__{left: %__MODULE__{color: :red, right: %__MODULE__{color: :black} = u} = z} = y) do
     %__MODULE__{
       u
       | color: :red,
@@ -295,9 +255,7 @@ defmodule Dasie.RedBlackTree do
               left: %__MODULE__{z.left | color: :red},
               right: u.left
           }),
-        right: %__MODULE__{y | left: u.right}
+        right: %__MODULE__{y | color: :black, left: u.right}
     }
   end
-
-  def balance_right(node), do: node
 end