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Design Circular Queue

Created: March 25, 2020 by [lek-tin]

Last updated: March 25, 2020

Design your implementation of the circular queue. The circular queue is a linear data structure in which the operations are performed based on FIFO (First In First Out) principle and the last position is connected back to the first position to make a circle. It is also called “Ring Buffer”.

One of the benefits of the circular queue is that we can make use of the spaces in front of the queue. In a normal queue, once the queue becomes full, we cannot insert the next element even if there is a space in front of the queue. But using the circular queue, we can use the space to store new values.

Your implementation should support following operations:

1. MyCircularQueue(k): Constructor, set the size of the queue to be k. 2. Front: Get the front item from the queue. If the queue is empty, return -1. 3. Rear: Get the last item from the queue. If the queue is empty, return -1. 4. enQueue(value): Insert an element into the circular queue. Return true if the operation is successful. 5. deQueue(): Delete an element from the circular queue. Return true if the operation is successful. 6. isEmpty(): Checks whether the circular queue is empty or not. 7. isFull(): Checks whether the circular queue is full or not.

Example

MyCircularQueue circularQueue = new MyCircularQueue(3); // set the size to be 3
circularQueue.enQueue(1);  // return true
circularQueue.enQueue(2);  // return true
circularQueue.enQueue(3);  // return true
circularQueue.enQueue(4);  // return false, the queue is full
circularQueue.Rear();  // return 3
circularQueue.isFull();  // return true
circularQueue.deQueue();  // return true
circularQueue.enQueue(4);  // return true
circularQueue.Rear();  // return 4

Note

  1. All values will be in the range of [0, 1000].
  2. The number of operations will be in the range of [1, 1000].
  3. Please do not use the built-in Queue library.

Solution (array)

class MyCircularQueue:

    def __init__(self, k: int):
        """
        Initialize your data structure here. Set the size of the queue to be k.
        """
        self.cap = k
        self.size = 0
        self.head = 0
        self.queue = [None for _ in range(k)]

    def enQueue(self, value: int) -> bool:
        """
        Insert an element into the circular queue. Return true if the operation is successful.
        """
        if self.isFull():
            return False
        newTail = (self.head + self.size) % self.cap
        self.queue[newTail] = value
        self.size += 1
        return True

    def deQueue(self) -> bool:
        """
        Delete an element from the circular queue. Return true if the operation is successful.
        """
        if self.isEmpty():
            return False

        self.queue[self.head] = None
        self.size -= 1
        self.head = (self.head + 1 ) % self.cap

        return True

    def Front(self) -> int:
        """
        Get the front item from the queue.
        """
        if self.isEmpty():
            return -1
        return self.queue[self.head]

    def Rear(self) -> int:
        """
        Get the last item from the queue.
        """
        if self.isEmpty():
            return -1
        tail = (self.head + self.size - 1) % self.cap
        return self.queue[tail]

    def isEmpty(self) -> bool:
        """
        Checks whether the circular queue is empty or not.
        """
        return self.size == 0

    def isFull(self) -> bool:
        """
        Checks whether the circular queue is full or not.
        """
        return self.size == self.cap


# Your MyCircularQueue object will be instantiated and called as such:
# obj = MyCircularQueue(k)
# param_1 = obj.enQueue(value)
# param_2 = obj.deQueue()
# param_3 = obj.Front()
# param_4 = obj.Rear()
# param_5 = obj.isEmpty()
# param_6 = obj.isFull()

Solution (linked list)