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Create priority_queue_using_list.py (#2435)
* Create priority_queue_using_list.py * Update priority_queue_using_list.py * Update priority_queue_using_list.py * Update priority_queue_using_list.py * Maximum queue size is 100 Co-authored-by: Christian Clauss <cclauss@me.com>
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Ashley Jeji George
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data_structures/queue/priority_queue_using_list.py
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232
data_structures/queue/priority_queue_using_list.py
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"""
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Pure Python implementations of a Fixed Priority Queue and an Element Priority Queue
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using Python lists.
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"""
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class OverFlowError(Exception):
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pass
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class UnderFlowError(Exception):
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pass
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class FixedPriorityQueue:
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"""
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Tasks can be added to a Priority Queue at any time and in any order but when Tasks
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are removed then the Task with the highest priority is removed in FIFO order. In
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code we will use three levels of priority with priority zero Tasks being the most
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urgent (high priority) and priority 2 tasks being the least urgent.
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Examples
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>>> fpq = FixedPriorityQueue()
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>>> fpq.enqueue(0, 10)
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>>> fpq.enqueue(1, 70)
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>>> fpq.enqueue(0, 100)
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>>> fpq.enqueue(2, 1)
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>>> fpq.enqueue(2, 5)
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>>> fpq.enqueue(1, 7)
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>>> fpq.enqueue(2, 4)
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>>> fpq.enqueue(1, 64)
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>>> fpq.enqueue(0, 128)
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>>> print(fpq)
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Priority 0: [10, 100, 128]
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Priority 1: [70, 7, 64]
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Priority 2: [1, 5, 4]
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>>> fpq.dequeue()
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10
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>>> fpq.dequeue()
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100
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>>> fpq.dequeue()
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128
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>>> fpq.dequeue()
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70
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>>> fpq.dequeue()
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7
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>>> print(fpq)
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Priority 0: []
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Priority 1: [64]
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Priority 2: [1, 5, 4]
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>>> fpq.dequeue()
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64
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>>> fpq.dequeue()
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1
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>>> fpq.dequeue()
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5
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>>> fpq.dequeue()
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4
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>>> fpq.dequeue()
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Traceback (most recent call last):
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...
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priority_queue_using_list.UnderFlowError: All queues are empty
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>>> print(fpq)
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Priority 0: []
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Priority 1: []
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Priority 2: []
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"""
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def __init__(self):
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self.queues = [
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[],
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[],
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[],
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]
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def enqueue(self, priority: int, data: int) -> None:
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"""
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Add an element to a queue based on its priority.
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If the priority is invalid ValueError is raised.
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If the queue is full an OverFlowError is raised.
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"""
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try:
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if len(self.queues[priority]) >= 100:
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raise OverflowError("Maximum queue size is 100")
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self.queues[priority].append(data)
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except IndexError:
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raise ValueError("Valid priorities are 0, 1, and 2")
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def dequeue(self) -> int:
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"""
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Return the highest priority element in FIFO order.
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If the queue is empty then an under flow exception is raised.
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"""
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for queue in self.queues:
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if queue:
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return queue.pop(0)
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raise UnderFlowError("All queues are empty")
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def __str__(self) -> str:
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return "\n".join(f"Priority {i}: {q}" for i, q in enumerate(self.queues))
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class ElementPriorityQueue:
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"""
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Element Priority Queue is the same as Fixed Priority Queue except that the value of
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the element itself is the priority. The rules for priorities are the same the as
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Fixed Priority Queue.
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>>> epq = ElementPriorityQueue()
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>>> epq.enqueue(10)
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>>> epq.enqueue(70)
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>>> epq.enqueue(4)
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>>> epq.enqueue(1)
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>>> epq.enqueue(5)
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>>> epq.enqueue(7)
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>>> epq.enqueue(4)
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>>> epq.enqueue(64)
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>>> epq.enqueue(128)
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>>> print(epq)
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[10, 70, 4, 1, 5, 7, 4, 64, 128]
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>>> epq.dequeue()
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1
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>>> epq.dequeue()
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4
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>>> epq.dequeue()
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4
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>>> epq.dequeue()
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5
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>>> epq.dequeue()
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7
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>>> epq.dequeue()
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10
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>>> print(epq)
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[70, 64, 128]
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>>> epq.dequeue()
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64
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>>> epq.dequeue()
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70
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>>> epq.dequeue()
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128
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>>> epq.dequeue()
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Traceback (most recent call last):
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...
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priority_queue_using_list.UnderFlowError: The queue is empty
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>>> print(epq)
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[]
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"""
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def __init__(self):
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self.queue = []
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def enqueue(self, data: int) -> None:
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"""
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This function enters the element into the queue
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If the queue is full an Exception is raised saying Over Flow!
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"""
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if len(self.queue) == 100:
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raise OverFlowError("Maximum queue size is 100")
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self.queue.append(data)
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def dequeue(self) -> int:
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"""
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Return the highest priority element in FIFO order.
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If the queue is empty then an under flow exception is raised.
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"""
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if not self.queue:
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raise UnderFlowError("The queue is empty")
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else:
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data = min(self.queue)
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self.queue.remove(data)
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return data
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def __str__(self) -> str:
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"""
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Prints all the elements within the Element Priority Queue
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"""
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return str(self.queue)
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def fixed_priority_queue():
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fpq = FixedPriorityQueue()
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fpq.enqueue(0, 10)
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fpq.enqueue(1, 70)
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fpq.enqueue(0, 100)
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fpq.enqueue(2, 1)
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fpq.enqueue(2, 5)
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fpq.enqueue(1, 7)
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fpq.enqueue(2, 4)
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fpq.enqueue(1, 64)
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fpq.enqueue(0, 128)
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print(fpq)
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print(fpq.dequeue())
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print(fpq.dequeue())
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print(fpq.dequeue())
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print(fpq.dequeue())
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print(fpq.dequeue())
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print(fpq)
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print(fpq.dequeue())
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print(fpq.dequeue())
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print(fpq.dequeue())
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print(fpq.dequeue())
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print(fpq.dequeue())
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def element_priority_queue():
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epq = ElementPriorityQueue()
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epq.enqueue(10)
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epq.enqueue(70)
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epq.enqueue(100)
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epq.enqueue(1)
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epq.enqueue(5)
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epq.enqueue(7)
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epq.enqueue(4)
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epq.enqueue(64)
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epq.enqueue(128)
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print(epq)
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print(epq.dequeue())
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print(epq.dequeue())
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print(epq.dequeue())
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print(epq.dequeue())
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print(epq.dequeue())
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print(epq)
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print(epq.dequeue())
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print(epq.dequeue())
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print(epq.dequeue())
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print(epq.dequeue())
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print(epq.dequeue())
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if __name__ == "__main__":
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fixed_priority_queue()
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element_priority_queue()
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