622.design-circular-queue.cpp

/*
 * @lc app=leetcode id=622 lang=cpp
 *
 * [622] Design Circular Queue
 *
 * https://leetcode.com/problems/design-circular-queue/description/
 *
 * algorithms
 * Medium (38.18%)
 * Total Accepted:    18.6K
 * Total Submissions: 48.7K
 * Testcase Example:  '["MyCircularQueue","enQueue","enQueue","enQueue","enQueue","Rear","isFull","deQueue","enQueue","Rear"]\n[[3],[1],[2],[3],[4],[],[],[],[4],[]]'
 *
 * 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.
 *
 *
 */
#include <vector>
#include <iostream>
using namespace std;

class MyCircularQueue
{
  private:
    vector<int> data;
    int size;
    // point to head element
    int p_head;
    // point to element after end
    int p_tail;
    // record num of element to diff empty vs full
    int nElement;

  public:
    /** Initialize your data structure here. Set the size of the queue to be k. */
    MyCircularQueue(int k)
    {
        data.resize(k);
        p_head = 0;
        p_tail = 0;
        nElement = 0;
        size = k;
    }

    /** Insert an element into the circular queue. Return true if the operation is successful. */
    bool enQueue(int value)
    {
        if (isFull())
        {
            return false;
        }
        data[p_tail] = value;
        nElement++;
        p_tail = (p_tail + 1) % size;
        return true;
    }

    /** Delete an element from the circular queue. Return true if the operation is successful. */
    bool deQueue()
    {
        if (isEmpty())
        {
            return false;
        }
        nElement--;
        p_head = (p_head + 1 + size) % size;
        return true;
    }

    /** Get the front item from the queue. */
    int Front()
    {
        return isEmpty() ? -1 : data[p_head];
    }

    /** Get the last item from the queue. */
    int Rear()
    {
        return isEmpty() ? -1 : data[(p_tail - 1 + size) % size];
    }

    /** Checks whether the circular queue is empty or not. */
    bool isEmpty()
    {
        return nElement == 0;
    }

    /** Checks whether the circular queue is full or not. */
    bool isFull()
    {
        return nElement == size;
    }
};

/**
 * Your MyCircularQueue object will be instantiated and called as such:
 * MyCircularQueue* obj = new MyCircularQueue(k);
 * bool param_1 = obj->enQueue(value);
 * bool param_2 = obj->deQueue();
 * int param_3 = obj->Front();
 * int param_4 = obj->Rear();
 * bool param_5 = obj->isEmpty();
 * bool param_6 = obj->isFull();
 */