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# The below license is invalid/void as the code that follows is not my | |
# own. This file is for demonstration purposes only. | |
# This is free and unencumbered software released into the public domain. | |
# | |
# Anyone is free to copy, modify, publish, use, compile, sell, or | |
# distribute this software, either in source code form or as a compiled | |
# binary, for any purpose, commercial or non-commercial, and by any | |
# means. | |
# | |
# In jurisdictions that recognize copyright laws, the author or authors | |
# of this software dedicate any and all copyright interest in the | |
# software to the public domain. We make this dedication for the benefit | |
# of the public at large and to the detriment of our heirs and | |
# successors. We intend this dedication to be an overt act of | |
# relinquishment in perpetuity of all present and future rights to this | |
# software under copyright law. | |
# | |
# 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 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. | |
# | |
# For more information, please refer to <http://unlicense.org/> | |
# Priority dictionary using binary heaps | |
# David Eppstein, UC Irvine, 8 Mar 2002 | |
from __future__ import generators | |
class priorityDictionary(dict): | |
def __init__(self): | |
'''Initialize priorityDictionary by creating binary heap | |
of pairs (value,key). Note that changing or removing a dict entry will | |
not remove the old pair from the heap until it is found by smallest() or | |
until the heap is rebuilt.''' | |
self.__heap = [] | |
dict.__init__(self) | |
def smallest(self): | |
'''Find smallest item after removing deleted items from heap.''' | |
if len(self) == 0: | |
raise IndexError, "smallest of empty priorityDictionary" | |
heap = self.__heap | |
while heap[0][1] not in self or self[heap[0][1]] != heap[0][0]: | |
lastItem = heap.pop() | |
insertionPoint = 0 | |
while 1: | |
smallChild = 2*insertionPoint+1 | |
if smallChild+1 < len(heap) and \ | |
heap[smallChild] > heap[smallChild+1]: | |
smallChild += 1 | |
if smallChild >= len(heap) or lastItem <= heap[smallChild]: | |
heap[insertionPoint] = lastItem | |
break | |
heap[insertionPoint] = heap[smallChild] | |
insertionPoint = smallChild | |
return heap[0][1] | |
def __iter__(self): | |
'''Create destructive sorted iterator of priorityDictionary.''' | |
def iterfn(): | |
while len(self) > 0: | |
x = self.smallest() | |
yield x | |
del self[x] | |
return iterfn() | |
def __setitem__(self,key,val): | |
'''Change value stored in dictionary and add corresponding | |
pair to heap. Rebuilds the heap if the number of deleted items grows | |
too large, to avoid memory leakage.''' | |
dict.__setitem__(self,key,val) | |
heap = self.__heap | |
if len(heap) > 2 * len(self): | |
self.__heap = [(v,k) for k,v in self.iteritems()] | |
self.__heap.sort() # builtin sort likely faster than O(n) heapify | |
else: | |
newPair = (val,key) | |
insertionPoint = len(heap) | |
heap.append(None) | |
while insertionPoint > 0 and \ | |
newPair < heap[(insertionPoint-1)//2]: | |
heap[insertionPoint] = heap[(insertionPoint-1)//2] | |
insertionPoint = (insertionPoint-1)//2 | |
heap[insertionPoint] = newPair | |
def setdefault(self,key,val): | |
'''Reimplement setdefault to call our customized __setitem__.''' | |
if key not in self: | |
self[key] = val | |
return self[key] |
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