# leetcode\_622

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.

## Solutions

1. **straight forward**
2. `lo` represents the front of the queue, `hi` represents element next to last element.
3. Use `k + 1` spaces to differentiate between empty(`lo == hi`) and full(`hi == lo - 1`)

```cpp
class MyCircularQueue {
public:
    /** Initialize your data structure here. Set the size of the queue to be k. */
    vector<int> q;
    int lo = 0, hi = 0, len = 0;
    MyCircularQueue(int k) : q(k + 1), len(k + 1) {

    }

    /** Insert an element into the circular queue. Return true if the operation is successful. */
    bool enQueue(int value) {
        if (!isFull()) {
            q[hi] = value;
            hi = (hi + 1) % len;
            return true;
        }
        else
            return false;
    }

    /** Delete an element from the circular queue. Return true if the operation is successful. */
    bool deQueue() {
        if (!isEmpty()) {
            lo = (lo + 1) % len;
            return true;
        }
        else
            return false;
    }

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

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

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

    /** Checks whether the circular queue is full or not. */
    bool isFull() {
        return hi == (lo + len - 1) % len;
    }
};

/**
 * 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();
 */
```