Create priority_queue_using_list.py

data_structures/queue/priority_queue.py

@@ -0,0 +1,248 @@
+"""
+Pure Python implementation of Priority Queue using lists
+"""
+
+
+class FixedPriorityQueue:
+    """
+    In a Priority Queue the elements are entred as an when the come
+    But while removing or deleting an element the highest priority element is deleted in FIFO fashion
+    Here the lowest integer has the highest priority.
+    Example:
+    priority(0) > priority(5)
+    priority(16) > priority(32)
+    Here as an example I have taken only 3 priorities viz. 0, 1, 2
+    0 Being the highest priority and 2 being the lowest
+    You can change the priorities as per your need
+
+    Examples
+    >>>FPQ = FixedPriorityQueue()
+    >>>FPQ.enqueue(0, 10)
+    >>>FPQ.enqueue(1, 70)
+    >>>FPQ.enqueue(0, 100)
+    >>>FPQ.enqueue(2, 1)
+    >>>FPQ.enqueue(2, 5)
+    >>>FPQ.enqueue(1, 7)
+    >>>FPQ.enqueue(2, 4)
+    >>>FPQ.enqueue(1, 64)
+    >>>FPQ.enqueue(0, 128)
+    >>>FPQ.print_queue()
+    Priority 0: [10, 100, 128]
+            Priority 1: [70, 7, 64]
+            Priority 2: [1, 5, 4]
+    >>>print(FPQ.dequeue())
+    10
+    >>>print(FPQ.dequeue())
+            100
+    >>>print(FPQ.dequeue())
+    128
+    >>>print(FPQ.dequeue())
+    70
+    >>>print(FPQ.dequeue())
+    7
+    >>>FPQ.print_queue()
+    Priority 0: []
+    Priority 1: [64]
+    Priority 2: [1, 5, 4]
+    >>>print(FPQ.dequeue())
+    64
+    >>>print(FPQ.dequeue())
+    1
+    >>>print(FPQ.dequeue())
+    5
+    >>>print(FPQ.dequeue())
+    4
+    >>>print(FPQ.dequeue())
+    Traceback (most recent call last):
+      File "Sample.py", line 117, in <module>
+            print(FPQ.dequeue())
+      File "Sample.py", line 58, in dequeue
+            raise Exception("Under Flow!")
+    Exception: Under Flow!
+    """
+
+    def __init__(self):
+        self.queue = [
+            [],
+            [],
+            [],
+        ]
+
+    def enqueue(self, priority, data):
+        """
+        This function enters the element into the FixedPriorityQueue based on its priority
+        If the priority is invalid an Exception is raised saying Invalid Priority!
+        If the FixedPriorityQueue is full an Exception is raised saying Over Flow!
+        """
+        if priority > 2:
+            raise Exception("Invalid Priority!")
+        elif len(self.queue[priority]) == 100:
+            raise Exception("Over Flow!")
+        else:
+            self.queue[priority].append(data)
+
+    def dequeue(self):
+        """
+        This function returns the highest priority element from the FixedPriorityQueue in FIFO fashion
+        If the FixedPriorityQueue is empty and this function is called then an exception is raised saying Under Flow!
+        """
+        if (
+            len(self.queue[0]) == 0
+            and len(self.queue[1]) == 0
+            and len(self.queue[2]) == 0
+        ):
+            raise Exception("Under Flow!")
+
+        if len(self.queue[0]) != 0:
+            return self.queue[0].pop(0)
+        elif len(self.queue[1]) != 0:
+            return self.queue[1].pop(0)
+        else:
+            return self.queue[2].pop(0)
+
+    def print_queue(self):
+        """
+        Prints each priority queue within the FixedPriorityQueue
+        """
+        print("Priority 0:", self.queue[0])
+        print("Priority 1:", self.queue[1])
+        print("Priority 2:", self.queue[2])
+
+
+class ElementPriorityQueue:
+    """
+    Element Priority Queue is the same as Fixed Priority Queue
+    The only difference being the value of the element itself is the priority
+    The rule for priorities are the same
+    The lowest integer has the highest priority.
+    Example:
+    priority(0) > priority(5)
+    priority(16) > priority(32)
+    You can change the priorities as per your need
+
+    >>>EPQ = ElementPriorityQueue()
+    >>>EPQ.enqueue(10)
+    >>>EPQ.enqueue(70)
+    >>>EPQ.enqueue(100)
+    >>>EPQ.enqueue(1)
+    >>>EPQ.enqueue(5)
+    >>>EPQ.enqueue(7)
+    >>>EPQ.enqueue(4)
+    >>>EPQ.enqueue(64)
+    >>>EPQ.enqueue(128)
+    >>>EPQ.print_queue()
+    [10, 70, 100, 1, 5, 7, 4, 64, 128]
+    >>>print(EPQ.dequeue())
+    1
+    >>>print(EPQ.dequeue())
+    4
+    >>>print(EPQ.dequeue())
+    5
+    >>>print(EPQ.dequeue())
+    7
+    >>>print(EPQ.dequeue())
+    10
+    >>>EPQ.print_queue()
+    [70, 100, 64, 128]
+    >>>print(EPQ.dequeue())
+    64
+    >>>print(EPQ.dequeue())
+    70
+    >>>print(EPQ.dequeue())
+    100
+    >>>print(EPQ.dequeue())
+    128
+    >>>print(EPQ.dequeue())
+    Traceback (most recent call last):
+              File "Sample.py", line 132, in <module>
+                    print(EPQ.dequeue())
+              File "Sample.py", line 100, in dequeue
+                    raise Exception("Under Flow!")
+            Exception: Under Flow!
+    """
+
+    def __init__(self):
+        self.queue = []
+
+    def enqueue(self, data):
+        """
+        This function enters the element into the ElementPriorityQueue based on its value
+        If the ElementPriorityQueue is full an Exception is raised saying Over Flow!
+        """
+        if len(self.queue) == 100:
+            raise Exception("Over Flow!")
+        else:
+            self.queue.append(data)
+
+    def dequeue(self):
+        """
+        This function returns the highest priority element from the ElementPriorityQueue in FIFO fashion.
+        If the ElementPriorityQueue is empty and this function is called then an exception is raised saying Under Flow!
+        """
+        if len(self.queue) == 0:
+            raise Exception("Under Flow!")
+        else:
+            data = min(self.queue)
+            self.queue.remove(data)
+            return data
+
+    def print_queue(self):
+        """
+        Prints all the elements within the Element Priority Queue
+        """
+        print(self.queue)
+
+
+def fixed_priority_queue():
+    FPQ = FixedPriorityQueue()
+    FPQ.enqueue(0, 10)
+    FPQ.enqueue(1, 70)
+    FPQ.enqueue(0, 100)
+    FPQ.enqueue(2, 1)
+    FPQ.enqueue(2, 5)
+    FPQ.enqueue(1, 7)
+    FPQ.enqueue(2, 4)
+    FPQ.enqueue(1, 64)
+    FPQ.enqueue(0, 128)
+    FPQ.print_queue()
+    print(FPQ.dequeue())
+    print(FPQ.dequeue())
+    print(FPQ.dequeue())
+    print(FPQ.dequeue())
+    print(FPQ.dequeue())
+    FPQ.print_queue()
+    print(FPQ.dequeue())
+    print(FPQ.dequeue())
+    print(FPQ.dequeue())
+    print(FPQ.dequeue())
+    print(FPQ.dequeue())
+
+
+def element_priority_queue():
+    EPQ = ElementPriorityQueue()
+    EPQ.enqueue(10)
+    EPQ.enqueue(70)
+    EPQ.enqueue(100)
+    EPQ.enqueue(1)
+    EPQ.enqueue(5)
+    EPQ.enqueue(7)
+    EPQ.enqueue(4)
+    EPQ.enqueue(64)
+    EPQ.enqueue(128)
+    EPQ.print_queue()
+    print(EPQ.dequeue())
+    print(EPQ.dequeue())
+    print(EPQ.dequeue())
+    print(EPQ.dequeue())
+    print(EPQ.dequeue())
+    EPQ.print_queue()
+    print(EPQ.dequeue())
+    print(EPQ.dequeue())
+    print(EPQ.dequeue())
+    print(EPQ.dequeue())
+    print(EPQ.dequeue())
+
+
+if __name__ == "__main__":
+    fixed_priority_queue()
+    element_priority_queue()