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622. Design Circular Queue (Medium)

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.

Companies:
Facebook, Amazon

Related Topics:
Design, Queue

Similar Questions:

Solution 1.

// OJ: https://leetcode.com/problems/design-circular-queue/
// Author: github.com/lzl124631x
// Time: O(1) for all
// Space: O(K)
class MyCircularQueue {
private:
    vector<int> v;
    int start = 0, len = 0;
public:
    MyCircularQueue(int k): v(k) {}
    bool enQueue(int value) {
        if (isFull()) return false;
        v[(start + len++) % v.size()] = value;
        return true;
    }
    bool deQueue() {
        if (isEmpty()) return false;
        start = (start + 1) % v.size();
        --len;
        return true;
    }
    int Front() {
        if (isEmpty()) return -1;
        return v[start];
    }
    int Rear() {
        if (isEmpty()) return -1;
        return v[(start + len - 1) % v.size()];
    }
    bool isEmpty() {
        return !len;
    }
    bool isFull() {
        return len == v.size();
    }
};