LC_103_DesignCircularQueue.cpp

#include <bits/stdc++.h>
using namespace std;

// Time Complexity: O(1)
// Space Complexity: O(N)
class MyCircularQueue
{
public:
    MyCircularQueue(int k)
    {
        // the queue holding the elements for the circular queue
        q.resize(k);
        // the number of elements in the circular queue
        cnt = 0;
        // queue size
        sz = k;
        // the idx of the head element
        headIdx = 0;
    }

    bool enQueue(int value)
    {
        // handle full case
        if (isFull())
            return false;
        // Given an array of size of 4, we can find the position to be inserted using the formula
        // targetIdx = (headIdx + cnt) % sz
        // e.g. [1, 2, 3, _]
        // headIdx = 0, cnt = 3, sz = 4, targetIdx = (0 + 3) % 4 = 3
        // e.g. [_, 2, 3, 4]
        // headIdx = 1, cnt = 3, sz = 4, targetIdx = (1 + 3) % 4 = 0
        q[(headIdx + cnt) % sz] = value;
        // increase the number of elements by 1
        cnt += 1;
        return true;
    }

    bool deQueue()
    {
        // handle empty case
        if (isEmpty())
            return false;
        // update the head index
        headIdx = (headIdx + 1) % sz;
        // decrease the number of elements by 1
        cnt -= 1;
        return true;
    }

    int Front()
    {
        // handle empty queue case
        if (isEmpty())
            return -1;
        // return the head element
        return q[headIdx];
    }

    int Rear()
    {
        // handle empty queue case
        if (isEmpty())
            return -1;
        // Given an array of size of 4, we can find the tailIdx using the formula
        // tailIdx = (headIdx + cnt - 1) % sz
        // e.g. [0 1 2] 3
        // headIdx = 0, cnt = 3, sz = 4, tailIdx = (0 + 3 - 1) % 4 = 2
        // e.g. 0 [1 2 3]
        // headIdx = 1, cnt = 3, sz = 4, tailIdx = (1 + 3 - 1) % 4 = 3
        // e.g. 0] 1 [2 3
        // headIdx = 2, cnt = 3, sz = 4, tailIdx = (2 + 3 - 1) % 4 = 0
        return q[(headIdx + cnt - 1) % sz];
    }

    bool isEmpty()
    {
        // no element in the queue
        return cnt == 0;
    }

    bool isFull()
    {
        // return true if the count is equal to the queue size
        // else return false
        return cnt == sz;
    }

private:
    int cnt, sz, headIdx;
    vector<int> q;
};

int main()
{
    MyCircularQueue *obj = new MyCircularQueue(3);
    cout << obj->enQueue(1) << endl;
    cout << obj->enQueue(2) << endl;
    cout << obj->enQueue(3) << endl;
    cout << obj->enQueue(4) << endl;
    cout << obj->Rear() << endl;
    cout << obj->isFull() << endl;
    cout << obj->deQueue() << endl;
    cout << obj->enQueue(4) << endl;
    cout << obj->Rear() << endl;
    return 0;
}