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source code for chapter 9
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‎ch09/__init__.py‎

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__all__ = ['adaptable_heap_priority_queue', 'heap_priority_queue', 'sorted_priority_queue', 'unsorted_priority_queue']

‎ch09/adaptable_heap_priority_queue.py‎

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# Copyright 2013, Michael H. Goldwasser
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#
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# Developed for use with the book:
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#
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# Data Structures and Algorithms in Python
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# Michael T. Goodrich, Roberto Tamassia, and Michael H. Goldwasser
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# John Wiley & Sons, 2013
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#
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# This program is free software: you can redistribute it and/or modify
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# it under the terms of the GNU General Public License as published by
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# the Free Software Foundation, either version 3 of the License, or
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# (at your option) any later version.
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#
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# This program is distributed in the hope that it will be useful,
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# but WITHOUT ANY WARRANTY; without even the implied warranty of
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# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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# GNU General Public License for more details.
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#
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# You should have received a copy of the GNU General Public License
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# along with this program. If not, see <http://www.gnu.org/licenses/>.
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from .heap_priority_queue import HeapPriorityQueue
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class AdaptableHeapPriorityQueue(HeapPriorityQueue):
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"""A locator-based priority queue implemented with a binary heap."""
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#------------------------------ nested Locator class ------------------------------
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class Locator(HeapPriorityQueue._Item):
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"""Token for locating an entry of the priority queue."""
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__slots__ = '_index' # add index as additional field
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def __init__(self, k, v, j):
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super().__init__(k,v)
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self._index = j
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#------------------------------ nonpublic behaviors ------------------------------
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# override swap to record new indices
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def _swap(self, i, j):
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super()._swap(i,j) # perform the swap
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self._data[i]._index = i # reset locator index (post-swap)
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self._data[j]._index = j # reset locator index (post-swap)
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def _bubble(self, j):
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if j > 0 and self._data[j] < self._data[self._parent(j)]:
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self._upheap(j)
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else:
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self._downheap(j)
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#------------------------------ public behaviors ------------------------------
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def add(self, key, value):
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"""Add a key-value pair."""
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token = self.Locator(key, value, len(self._data)) # initiaize locator index
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self._data.append(token)
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self._upheap(len(self._data) - 1)
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return token
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def update(self, loc, newkey, newval):
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"""Update the key and value for the entry identified by Locator loc."""
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j = loc._index
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if not (0 <= j < len(self) and self._data[j] is loc):
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raise ValueError('Invalid locator')
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loc._key = newkey
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loc._value = newval
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self._bubble(j)
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def remove(self, loc):
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"""Remove and return the (k,v) pair identified by Locator loc."""
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j = loc._index
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if not (0 <= j < len(self) and self._data[j] is loc):
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raise ValueError('Invalid locator')
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if j == len(self) - 1: # item at last position
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self._data.pop() # just remove it
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else:
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self._swap(j, len(self)-1) # swap item to the last position
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self._data.pop() # remove it from the list
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self._bubble(j) # fix item displaced by the swap
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return (loc._key, loc._value)

‎ch09/heap_priority_queue.py‎

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# Copyright 2013, Michael H. Goldwasser
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#
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# Developed for use with the book:
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#
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# Data Structures and Algorithms in Python
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# Michael T. Goodrich, Roberto Tamassia, and Michael H. Goldwasser
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# John Wiley & Sons, 2013
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#
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# This program is free software: you can redistribute it and/or modify
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# it under the terms of the GNU General Public License as published by
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# the Free Software Foundation, either version 3 of the License, or
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# (at your option) any later version.
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#
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# This program is distributed in the hope that it will be useful,
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# but WITHOUT ANY WARRANTY; without even the implied warranty of
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# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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# GNU General Public License for more details.
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#
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# You should have received a copy of the GNU General Public License
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# along with this program. If not, see <http://www.gnu.org/licenses/>.
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from .priority_queue_base import PriorityQueueBase
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from ..exceptions import Empty
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class HeapPriorityQueue(PriorityQueueBase): # base class defines _Item
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"""A min-oriented priority queue implemented with a binary heap."""
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#------------------------------ nonpublic behaviors ------------------------------
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def _parent(self, j):
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return (j-1) // 2
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def _left(self, j):
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return 2*j + 1
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def _right(self, j):
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return 2*j + 2
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def _has_left(self, j):
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return self._left(j) < len(self._data) # index beyond end of list?
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def _has_right(self, j):
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return self._right(j) < len(self._data) # index beyond end of list?
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def _swap(self, i, j):
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"""Swap the elements at indices i and j of array."""
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self._data[i], self._data[j] = self._data[j], self._data[i]
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def _upheap(self, j):
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parent = self._parent(j)
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if j > 0 and self._data[j] < self._data[parent]:
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self._swap(j, parent)
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self._upheap(parent) # recur at position of parent
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def _downheap(self, j):
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if self._has_left(j):
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left = self._left(j)
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small_child = left # although right may be smaller
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if self._has_right(j):
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right = self._right(j)
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if self._data[right] < self._data[left]:
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small_child = right
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if self._data[small_child] < self._data[j]:
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self._swap(j, small_child)
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self._downheap(small_child) # recur at position of small child
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#------------------------------ public behaviors ------------------------------
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def __init__(self):
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"""Create a new empty Priority Queue."""
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self._data = []
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def __len__(self):
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"""Return the number of items in the priority queue."""
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return len(self._data)
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def add(self, key, value):
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"""Add a key-value pair to the priority queue."""
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self._data.append(self._Item(key, value))
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self._upheap(len(self._data) - 1) # upheap newly added position
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def min(self):
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"""Return but do not remove (k,v) tuple with minimum key.
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Raise Empty exception if empty.
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"""
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if self.is_empty():
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raise Empty('Priority queue is empty.')
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item = self._data[0]
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return (item._key, item._value)
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def remove_min(self):
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"""Remove and return (k,v) tuple with minimum key.
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Raise Empty exception if empty.
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"""
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if self.is_empty():
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raise Empty('Priority queue is empty.')
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self._swap(0, len(self._data) - 1) # put minimum item at the end
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item = self._data.pop() # and remove it from the list;
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self._downheap(0) # then fix new root
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return (item._key, item._value)

‎ch09/priority_queue_base.py‎

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# Copyright 2013, Michael H. Goldwasser
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#
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# Developed for use with the book:
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#
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# Data Structures and Algorithms in Python
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# Michael T. Goodrich, Roberto Tamassia, and Michael H. Goldwasser
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# John Wiley & Sons, 2013
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#
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# This program is free software: you can redistribute it and/or modify
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# it under the terms of the GNU General Public License as published by
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# the Free Software Foundation, either version 3 of the License, or
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# (at your option) any later version.
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#
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# This program is distributed in the hope that it will be useful,
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# but WITHOUT ANY WARRANTY; without even the implied warranty of
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# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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# GNU General Public License for more details.
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#
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# You should have received a copy of the GNU General Public License
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# along with this program. If not, see <http://www.gnu.org/licenses/>.
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from ..exceptions import Empty
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class PriorityQueueBase:
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"""Abstract base class for a priority queue."""
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#------------------------------ nested _Item class ------------------------------
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class _Item:
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"""Lightweight composite to store priority queue items."""
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__slots__ = '_key', '_value'
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def __init__(self, k, v):
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self._key = k
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self._value = v
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def __lt__(self, other):
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return self._key < other._key # compare items based on their keys
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def __repr__(self):
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return '({0},{1})'.format(self._key, self._value)
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#------------------------------ public behaviors ------------------------------
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def is_empty(self): # concrete method assuming abstract len
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"""Return True if the priority queue is empty."""
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return len(self) == 0
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def __len__(self):
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"""Return the number of items in the priority queue."""
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raise NotImplementedError('must be implemented by subclass')
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def add(self, key, value):
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"""Add a key-value pair."""
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raise NotImplementedError('must be implemented by subclass')
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def min(self):
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"""Return but do not remove (k,v) tuple with minimum key.
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Raise Empty exception if empty.
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"""
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raise NotImplementedError('must be implemented by subclass')
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def remove_min(self):
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"""Remove and return (k,v) tuple with minimum key.
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Raise Empty exception if empty.
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"""
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raise NotImplementedError('must be implemented by subclass')

‎ch09/sorted_priority_queue.py‎

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# Copyright 2013, Michael H. Goldwasser
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#
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# Developed for use with the book:
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#
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# Data Structures and Algorithms in Python
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# Michael T. Goodrich, Roberto Tamassia, and Michael H. Goldwasser
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# John Wiley & Sons, 2013
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#
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# This program is free software: you can redistribute it and/or modify
10+
# it under the terms of the GNU General Public License as published by
11+
# the Free Software Foundation, either version 3 of the License, or
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# (at your option) any later version.
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#
14+
# This program is distributed in the hope that it will be useful,
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# but WITHOUT ANY WARRANTY; without even the implied warranty of
16+
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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# GNU General Public License for more details.
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#
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# You should have received a copy of the GNU General Public License
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# along with this program. If not, see <http://www.gnu.org/licenses/>.
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from .priority_queue_base import PriorityQueueBase
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from ..ch07.positional_list import PositionalList
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from ..exceptions import Empty
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class SortedPriorityQueue(PriorityQueueBase): # base class defines _Item
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"""A min-oriented priority queue implemented with a sorted list."""
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#------------------------------ public behaviors ------------------------------
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def __init__(self):
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"""Create a new empty Priority Queue."""
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self._data = PositionalList()
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def __len__(self):
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"""Return the number of items in the priority queue."""
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return len(self._data)
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def add(self, key, value):
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"""Add a key-value pair."""
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newest = self._Item(key, value) # make new item instance
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walk = self._data.last() # walk backward looking for smaller key
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while walk is not None and newest < walk.element():
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walk = self._data.before(walk)
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if walk is None:
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self._data.add_first(newest) # new key is smallest
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else:
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self._data.add_after(walk, newest) # newest goes after walk
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def min(self):
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"""Return but do not remove (k,v) tuple with minimum key.
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Raise Empty exception if empty.
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"""
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if self.is_empty():
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raise Empty('Priority queue is empty.')
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p = self._data.first()
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item = p.element()
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return (item._key, item._value)
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def remove_min(self):
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"""Remove and return (k,v) tuple with minimum key.
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Raise Empty exception if empty.
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"""
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if self.is_empty():
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raise Empty('Priority queue is empty.')
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item = self._data.delete(self._data.first())
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return (item._key, item._value)

‎ch09/unsorted_priority_queue.py‎

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# Copyright 2013, Michael H. Goldwasser
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#
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# Developed for use with the book:
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#
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# Data Structures and Algorithms in Python
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# Michael T. Goodrich, Roberto Tamassia, and Michael H. Goldwasser
7+
# John Wiley & Sons, 2013
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#
9+
# This program is free software: you can redistribute it and/or modify
10+
# it under the terms of the GNU General Public License as published by
11+
# the Free Software Foundation, either version 3 of the License, or
12+
# (at your option) any later version.
13+
#
14+
# This program is distributed in the hope that it will be useful,
15+
# but WITHOUT ANY WARRANTY; without even the implied warranty of
16+
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
17+
# GNU General Public License for more details.
18+
#
19+
# You should have received a copy of the GNU General Public License
20+
# along with this program. If not, see <http://www.gnu.org/licenses/>.
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from .priority_queue_base import PriorityQueueBase
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from ..ch07.positional_list import PositionalList
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from ..exceptions import Empty
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class UnsortedPriorityQueue(PriorityQueueBase): # base class defines _Item
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"""A min-oriented priority queue implemented with an unsorted list."""
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#----------------------------- nonpublic behavior -----------------------------
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def _find_min(self):
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"""Return Position of item with minimum key."""
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if self.is_empty(): # is_empty inherited from base class
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raise Empty('Priority queue is empty')
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small = self._data.first()
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walk = self._data.after(small)
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while walk is not None:
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if walk.element() < small.element():
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small = walk
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walk = self._data.after(walk)
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return small
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#------------------------------ public behaviors ------------------------------
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def __init__(self):
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"""Create a new empty Priority Queue."""
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self._data = PositionalList()
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def __len__(self):
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"""Return the number of items in the priority queue."""
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return len(self._data)
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def add(self, key, value):
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"""Add a key-value pair."""
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self._data.add_last(self._Item(key, value))
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def min(self):
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"""Return but do not remove (k,v) tuple with minimum key.
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Raise Empty exception if empty.
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"""
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p = self._find_min()
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item = p.element()
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return (item._key, item._value)
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def remove_min(self):
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"""Remove and return (k,v) tuple with minimum key.
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Raise Empty exception if empty.
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"""
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p = self._find_min()
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item = self._data.delete(p)
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return (item._key, item._value)

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