【leetcode】622. Design Circular Queue

题目如下：

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:

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

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

解题思路：用list就能搞定了。

代码如下：

class MyCircularQueue(object):

    def __init__(self, k):
        """
        Initialize your data structure here. Set the size of the queue to be k.
        :type k: int
        """
        self.capacity = k
        self.l = []

    def enQueue(self, value):
        """
        Insert an element into the circular queue. Return true if the operation is successful.
        :type value: int
        :rtype: bool
        """
        if len(self.l) >= self.capacity:
            return False
        self.l.append(value)
        return True

    def deQueue(self):
        """
        Delete an element from the circular queue. Return true if the operation is successful.
        :rtype: bool
        """
        if len(self.l) == 0:
            return False
        self.l.pop(0)
        return True

    def Front(self):
        """
        Get the front item from the queue.
        :rtype: int
        """
        return self.l[0] if len(self.l) > 0 else -1

    def Rear(self):
        """
        Get the last item from the queue.
        :rtype: int
        """
        return self.l[-1] if len(self.l) > 0 else -1

    def isEmpty(self):
        """
        Checks whether the circular queue is empty or not.
        :rtype: bool
        """
        return len(self.l) == 0

    def isFull(self):
        """
        Checks whether the circular queue is full or not.
        :rtype: bool
        """
        return len(self.l) == self.capacity