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# add to heapq things like removing any item and changing key value

# implementation of priority queue to support contains, change_task_priority

# and remove_task in log time

from heapq import *

class PriorityQueue(object):

def __init__(self, is_min_heap):

self.pq = []

self.entry_finder = {}

if(is_min_heap is True):

self.mul = 1

else :

self.mul = -1

def contains_task(self, task):

if task in self.entry_finder:

return True

else:

return False

def get_task_priority(self, task):

if task in self.entry_finder:

return (self.entry_finder[task])[0]

raise ValueError("task does not exist")

def add_task(self, priority, task):

if task in self.entry_finder:

raise KeyError("Key already exists")

entry = [self.mul*priority, False, task]

self.entry_finder[task] = entry

heappush(self.pq, entry)

def change_task_priority(self, priority, task):

if task not in self.entry_finder:

raise KeyError("Task not found")

self.remove_task(task)

entry = [self.mul*priority, False, task]

self.entry_finder[task] = entry

heappush(self.pq, entry)

def remove_task(self, task):

entry = self.entry_finder.pop(task)

entry[1] = True

def pop_task(self):

while self.pq:

priority, removed, task = heappop(self.pq)

if removed is False:

del self.entry_finder[task]

return task

raise KeyError("pop from an empty priority queue")

def peek_task(self):

while self.pq:

priority, removed, task = tuple(heappop(self.pq))

if removed is False:

heappush(self.pq, [priority, False, task])

return task

raise KeyError("pop from an empty priority queue")

def is_empty(self):

try:

self.peek_task()

return False

except KeyError:

return True

def __str__(self):

return str(self.entry_finder) + " " + str(self.pq)

if __name__ == '__main__':

task1 = "Tushar"

task2 = "Roy"

task3 = "is"

task4 = "coder"

min_pq = PriorityQueue(True)

min_pq.add_task(1, task1)

min_pq.add_task(3, task2)

min_pq.add_task(6, task3)

min_pq.add_task(7, task4)

print(min_pq.contains_task(task3))

print(min_pq.get_task_priority(task3))

print(min_pq)

while min_pq.is_empty() is False:

print(min_pq.pop_task())

max_pq = PriorityQueue(False)

max_pq.add_task(1, task1)

max_pq.add_task(3, task2)

max_pq.add_task(6, task3)

max_pq.add_task(7, task4)

while max_pq.is_empty() is False:

print(max_pq.pop_task())