"delete_fixup" optimization (keon#873)

* "delete_fixup" optimization * node_min.parent != node -> node_min.parent is not node

Author: izveigor

algorithms/tree/red_black_tree/red_black_tree.py

@@ -194,7 +194,7 @@ def delete(self, node):
  node_color = node_min.color
  temp_node = node_min.right
  ## 
- if node_min.parent != node:
+ if node_min.parent is not node:
  self.transplant(node_min, node_min.right)
  node_min.right = node.right
  node_min.right.parent = node_min
@@ -208,9 +208,9 @@ def delete(self, node):
 
  def delete_fixup(self, node):
  # 4 cases
- while node != self.root and node.color == 0:
+ while node is not self.root and node.color == 0:
  # node is not root and color is black
- if node == node.parent.left:
+ if node is node.parent.left:
  # node is left node
  node_brother = node.parent.right