622. Design Circular Queue

• categories: Code, Interview Question, leetcode, Medium
• source: https://leetcode.com/problems/design-circular-queue/description
• topics: Array, Linked List

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.

Implement the MyCircularQueue class:

• MyCircularQueue(k) Initializes the object with the size of the queue to be k.
• int Front() Gets the front item from the queue. If the queue is empty, return -1.
• int Rear() Gets the last item from the queue. If the queue is empty, return -1.
• boolean enQueue(int value) Inserts an element into the circular queue. Return true if the operation is successful.
• boolean deQueue() Deletes an element from the circular queue. Return true if the operation is successful.
• boolean isEmpty() Checks whether the circular queue is empty or not.
• boolean isFull() Checks whether the circular queue is full or not.

You must solve the problem without using the built-in queue data structure in your programming language.

class MyCircularQueue(object):
    def __init__(self, k):
        """
        :type k: int
        """
        self.head = 0
        self.buffer = [0] * k
        self.count = 0
        self.capacity = k
        
    def enQueue(self, value):
        """
        :type value: int
        :rtype: bool
        """
        if self.count == self.capacity:
            return False
        self.count += 1
        self.buffer[(self.head + self.count - 1) % self.capacity] = value
        return True
 
    def deQueue(self):
        """
        :rtype: bool
        """
        if self.count == 0:
            return False
        self.head = (self.head + 1) % self.capacity
        self.count -= 1
        return True
 
    def Front(self):
        """
        :rtype: int
        """
        if self.count == 0:
            return -1
        return self.buffer[self.head]
 
    def Rear(self):
        """
        :rtype: int
        """
        if self.count == 0:
            return -1
        return self.buffer[(self.head + self.count - 1) % self.capacity]
 
    def isEmpty(self):
        """
        :rtype: bool
        """
        return bool(self.count == 0)
        
 
    def isFull(self):
        """
        :rtype: bool
        """
        return bool(self.count == self.capacity)
 
 
# 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()

Problems and solutions :

• Thread safeness - should use threading.Lock() to ensure
• Memory allocated in the beginning, we may use Linked List to improve it