622. Design Circular Queue

O(1) time O(k) space
用左闭右开区间[b, e)

class MyCircularQueue {
public:
    /** Initialize your data structure here. Set the size of the queue to be k. */
    MyCircularQueue(int k) : k(k) {
        q.resize(k);
    }

    /** Insert an element into the circular queue. Return true if the operation is successful. */
    bool enQueue(int value) {
        if (isFull()) return false;
        q[e] = value;
        e = (e + 1) % k;
        is_empty = false;
        is_full = b == e;
        return true;
    }

    /** Delete an element from the circular queue. Return true if the operation is successful. */
    bool deQueue() {
        if (isEmpty()) return false;
        b = (b + 1) % k;
        is_full = false;
        is_empty = b == e;
        return true;
    }

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

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

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

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

    int b = 0, e = 0, k;
    vector<int> q;
    bool is_full = false, is_empty = true;
};

/**
 * 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();
 */