BST License

"""
Binary Search Tree: A sorted collection of values that supports
efficient insertion, deletion, and minimum/maximum value finding.
"""
# Copyright (C) 2008 by Edward Loper
# 
# Permission is hereby granted, free of charge, to any person obtaining a copy
# of this software and associated documentation files (the "Software"), to deal
# in the Software without restriction, including without limitation the rights
# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
# copies of the Software, and to permit persons to whom the Software is
# furnished to do so, subject to the following conditions:
# 
# The above copyright notice and this permission notice shall be included in
# all copies or substantial portions of the Software.
# 
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
# THE SOFTWARE.


# IMPLEMENTATION NOTES:
#
# Internally, we represent tree nodes using Python lists.  These lists
# may either be empty (for empty nodes) or may have length four (for
# non-empty nodes).  The non-empty nodes contain:
#
#     [left_child, right_child, value, sort_key]
#
# Using lists rather than a node class more than doubles the overall
# performance in the benchmarks that I have run.
#
# The sort key is always accessed as node[-1].  This allows us to
# optimize the case where the sort key is identical to the value, by
# encoding such nodes as simply:
#
#     [left_child, right_child, value]
#
# The following constants are used to access the pieces of each search
# node.  If the constant-binding optimization recipe (which can be
# downloaded from <http://code.activestate.com/recipes/277940/>) is
# available, then it is used to replace these constants at
# import-time, increasing the binary search tree efficiency by 3-5%.