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Starting a redblacktree.py module for Section 3.4, Exercise 4.
author Brian Neal <bgneal@gmail.com>
date Tue, 18 Dec 2012 19:54:04 -0600
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14:bc2c07a059be 15:b163f18eaf92
1 """A red-black tree for Section 3.4, Exercise 4 in Allen Downey's _Think
2 Complexity_ book.
3
4 http://greenteapress.com/complexity
5
6 Copyright (C) 2012 Brian G. Neal.
7
8 Permission is hereby granted, free of charge, to any person obtaining a copy of
9 this software and associated documentation files (the "Software"), to deal in
10 the Software without restriction, including without limitation the rights to
11 use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
12 the Software, and to permit persons to whom the Software is furnished to do so,
13 subject to the following conditions:
14
15 The above copyright notice and this permission notice shall be included in all
16 copies or substantial portions of the Software.
17
18 THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
19 IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
20 FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
21 COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
22 IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
23 CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
24
25 """
26
27 BLACK, RED = range(1)
28
29 class Node(object):
30 """A node class for red-black trees.
31
32 A node has an optional parent, and optional left and right children. Each
33 node also has a color, either red or black. A node has a key and an optional
34 value. The key is used to order the red black tree by calling the "<"
35 operator when comparing keys.
36
37 In a red-black tree, nil children are always considered black.
38
39 """
40
41 def __init__(self, key, color=RED, value=None):
42 self.key = key
43 self.value = value
44 self.color = color
45
46 self.parent = None
47 self.left = None
48 self.right = None
49
50 @property
51 def grandparent(self):
52 """Return the grandparent of this node, or None if it does not exist."""
53 return self.parent.parent if self.parent else None
54
55 @property
56 def uncle(self):
57 """Return this node's uncle if it exists, or None if not.
58
59 An uncle is a parent's sibling.
60
61 """
62 g = self.grandparent
63 if g:
64 return g.left if g.right is self.parent else g.right
65 return None