[leetcode] 622. Design Circular Queue

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. 

 

Example 1:

Input
["MyCircularQueue", "enQueue", "enQueue", "enQueue", "enQueue", "Rear", "isFull", "deQueue", "enQueue", "Rear"]
[[3], [1], [2], [3], [4], [], [], [], [4], []]
Output
[null, true, true, true, false, 3, true, true, true, 4]

Explanation
MyCircularQueue myCircularQueue = new MyCircularQueue(3);
myCircularQueue.enQueue(1); // return True
myCircularQueue.enQueue(2); // return True
myCircularQueue.enQueue(3); // return True
myCircularQueue.enQueue(4); // return False
myCircularQueue.Rear();     // return 3
myCircularQueue.isFull();   // return True
myCircularQueue.deQueue();  // return True
myCircularQueue.enQueue(4); // return True
myCircularQueue.Rear();     // return 4

 

Constraints:

• 1 <= k <= 1000
• 0 <= value <= 1000
• At most 3000 calls will be made to enQueue, deQueue, Front, Rear, isEmpty, and isFull.

 

 

class MyCircularQueue(object):

    def __init__(self, k):
        """
        :type k: int
        """
        self.q = [None] * k 
        self.maxlen = k 
        self.p1 = 0
        self.p2 = 0
        

    def enQueue(self, value):
        """
        :type value: int
        :rtype: bool
        """
        if self.q[self.p2] is None: 
            self.q[self.p2] = value 
            self.p2 = ( self.p2 + 1 ) % self.maxlen 
            return True
        else: 
            return False 
        

    def deQueue(self):
        """
        :rtype: bool
        """
        if self.q[self.p1] is None:
            return False
        else: 
            self.q[self.p1] = None
            self.p1 = ( self.p1 + 1 ) % self.maxlen 
            return True 
        

    def Front(self):
        """
        :rtype: int
        """
        return -1 if self.q[self.p1] is None else self.q[self.p1]
        

    def Rear(self):
        """
        :rtype: int
        """
        return -1 if self.q[self.p2 - 1] is None else self.q[self.p2 - 1]
        

    def isEmpty(self):
        """
        :rtype: bool
        """
        return self.p1 == self.p2 and self.q[self.p1] is None 
        

    def isFull(self):
        """
        :rtype: bool
        """
        return self.p1 == self.p2 and self.q[self.p1] is not None 
        


# 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()