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.

Implementation 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.

Approach 1: Array

Written by@wkw

// 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;
};

/**
 * 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();
 */

0622 - Design Circular Queue (Medium)

Problem Link

Problem Statement

Approach 1: Array

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