641. 设计循环双端队列

数组实现的循环双端队列

public class MyCircularDeque {

    // 1、不用设计成动态数组，使用静态数组即可
    // 2、设计 head 和 tail 指针变量
    // 3、head == tail 成立的时候表示队列为空
    // 4、tail + 1 == head

    private int capacity;
    private int[] arr;
    private int front;
    private int rear;

    /**
     * Initialize your data structure here. Set the size of the deque to be k.
     */
    public MyCircularDeque(int k) {
        capacity = k + 1;
        arr = new int[capacity];

        // 头部指向第 1 个存放元素的位置
        // 插入时，先减，再赋值
        // 删除时，索引 +1（注意取模）
        front = 0;
        // 尾部指向下一个插入元素的位置
        // 插入时，先赋值，再加
        // 删除时，索引 -1（注意取模）
        rear = 0;
    }

    /**
     * Adds an item at the front of Deque. Return true if the operation is successful.
     */
    public boolean insertFront(int value) {
        if (isFull()) {
            return false;
        }
        front = (front - 1 + capacity) % capacity;
        arr[front] = value;
        return true;
    }

    /**
     * Adds an item at the rear of Deque. Return true if the operation is successful.
     */
    public boolean insertLast(int value) {
        if (isFull()) {
            return false;
        }
        arr[rear] = value;
        rear = (rear + 1) % capacity;
        return true;
    }

    /**
     * Deletes an item from the front of Deque. Return true if the operation is successful.
     */
    public boolean deleteFront() {
        if (isEmpty()) {
            return false;
        }
        // front 被设计在数组的开头，所以是 +1
        front = (front + 1) % capacity;
        return true;
    }

    /**
     * Deletes an item from the rear of Deque. Return true if the operation is successful.
     */
    public boolean deleteLast() {
        if (isEmpty()) {
            return false;
        }
        // rear 被设计在数组的末尾，所以是 -1
        rear = (rear - 1 + capacity) % capacity;
        return true;
    }

    /**
     * Get the front item from the deque.
     */
    public int getFront() {
        if (isEmpty()) {
            return -1;
        }
        return arr[front];
    }

    /**
     * Get the last item from the deque.
     */
    public int getRear() {
        if (isEmpty()) {
            return -1;
        }
        // 当 rear 为 0 时防止数组越界
        return arr[(rear - 1 + capacity) % capacity];
    }

    /**
     * Checks whether the circular deque is empty or not.
     */
    public boolean isEmpty() {
        return front == rear;
    }

    /**
     * Checks whether the circular deque is full or not.
     */
    public boolean isFull() {
        // 注意：这个设计是非常经典的做法
        return (rear + 1) % capacity == front;
    }
}

作者：liweiwei1419
链接：https://leetcode-cn.com/problems/design-circular-deque/solution/shu-zu-shi-xian-de-xun-huan-shuang-duan-dui-lie-by/
来源：力扣（LeetCode）
著作权归作者所有。商业转载请联系作者获得授权，非商业转载请注明出处。

/**
 * Your MyCircularDeque object will be instantiated and called as such:
 * MyCircularDeque obj = new MyCircularDeque(k);
 * boolean param_1 = obj.insertFront(value);
 * boolean param_2 = obj.insertLast(value);
 * boolean param_3 = obj.deleteFront();
 * boolean param_4 = obj.deleteLast();
 * int param_5 = obj.getFront();
 * int param_6 = obj.getRear();
 * boolean param_7 = obj.isEmpty();
 * boolean param_8 = obj.isFull();
 */