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September 18, 2018 20:04
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Priority Queue implementation
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import heapq | |
from pythonds.trees.binheap import BinHeap | |
from queue import PriorityQueue | |
""" What is a Prioruty Queue and Why to use it: | |
http://btechsmartclass.com/DS/U3_T6.html | |
""" | |
""" Inspirations: | |
https://dbader.org/blog/priority-queues-in-python | |
http://interactivepython.org/courselib/static/pythonds/Trees/BinaryHeapOperations.html | |
""" | |
## Using usual Lists to implement a Priority Queue ## | |
## This method is slowest as it takes O(n) for insertion | |
## and O(n*logn) for sorting | |
class MaxPQ: | |
def __init__(self): | |
self.pq = [] | |
def insert(self, val): | |
self.pq.append(val) | |
def _FindMax(self): | |
s = sorted(self.pq, reverse = True) | |
return s[0] | |
def remove(self): | |
m = self._FindMax() | |
self.pq.remove(m) | |
return m | |
def __repr__(self): | |
return repr(self.pq) | |
def __str__(self): | |
return "MaxPQ: {}".format(str(self.pq)) | |
## Test Case for MaxPQ ## | |
# p = MaxPQ() | |
# p.insert(3) | |
# p.insert(4) | |
# p.insert(1) | |
# p.insert(10) | |
# p.insert(2) | |
# print(p.remove()) | |
# print(p.remove()) | |
# print(p) | |
## Using PriorityQueue ## | |
#pq = PriorityQueue({1: "a", 2: "b", 3: "c"}) | |
pq = PriorityQueue() | |
pq.put((2, 'code')) | |
pq.put((1, 'sleep')) | |
pq.put((3, 'eat')) | |
while not pq.empty(): | |
print(pq.get()) | |
## Using Binary Heap to implement Priority queue ## | |
p1 = [(2, "code"), (1, "eat"), (3, "sleep")] | |
heapq.heapify(p1) | |
p2 = [] | |
heapq.heappush(p2, (1, "code")) | |
heapq.heappush(p2, (2, "eat")) | |
print("p1", p1) | |
while p1: | |
print(heapq.heappop(p1)) | |
print("p2", p2) | |
while p2: | |
print(heapq.heappop(p2)) | |
## Using pythonds module ## | |
p3 = BinHeap() | |
p3.insert(1) | |
p3.insert(2) | |
p3.insert(4) | |
print("p3", p3) | |
print(p3.delMin()) |
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