[LeetCode] 641. Design Circular Deque

Design your implementation of the circular double-ended queue (deque).

Implement the MyCircularDeque class:
MyCircularDeque(int k) Initializes the deque with a maximum size of k.
boolean insertFront() Adds an item at the front of Deque. Returns true if the operation is successful, or false otherwise.
boolean insertLast() Adds an item at the rear of Deque. Returns true if the operation is successful, or false otherwise.
boolean deleteFront() Deletes an item from the front of Deque. Returns true if the operation is successful, or false otherwise.
boolean deleteLast() Deletes an item from the rear of Deque. Returns true if the operation is successful, or false otherwise.
int getFront() Returns the front item from the Deque. Returns -1 if the deque is empty.
int getRear() Returns the last item from Deque. Returns -1 if the deque is empty.
boolean isEmpty() Returns true if the deque is empty, or false otherwise.
boolean isFull() Returns true if the deque is full, or false otherwise.

Example 1:
Input
[“MyCircularDeque”, “insertLast”, “insertLast”, “insertFront”, “insertFront”, “getRear”, “isFull”, “deleteLast”, “insertFront”, “getFront”]
[[3], [1], [2], [3], [4], [], [], [], [4], []]
Output
[null, true, true, true, false, 2, true, true, true, 4]

Explanation
MyCircularDeque myCircularDeque = new MyCircularDeque(3);
myCircularDeque.insertLast(1); // return True
myCircularDeque.insertLast(2); // return True
myCircularDeque.insertFront(3); // return True
myCircularDeque.insertFront(4); // return False, the queue is full.
myCircularDeque.getRear(); // return 2
myCircularDeque.isFull(); // return True
myCircularDeque.deleteLast(); // return True
myCircularDeque.insertFront(4); // return True
myCircularDeque.getFront(); // return 4

Constraints:
1 <= k <= 1000
0 <= value <= 1000
At most 2000 calls will be made to insertFront, insertLast, deleteFront, deleteLast, getFront, getRear, isEmpty, isFull.

设计循环双端队列。

设计实现双端队列。
实现 MyCircularDeque 类:

MyCircularDeque(int k) ：构造函数,双端队列最大为 k 。

boolean insertFront()：将一个元素添加到双端队列头部。如果操作成功返回 true ，否则返回 false 。

boolean insertLast() ：将一个元素添加到双端队列尾部。如果操作成功返回 true ，否则返回 false 。

boolean deleteFront() ：从双端队列头部删除一个元素。如果操作成功返回 true ，否则返回 false 。

boolean deleteLast() ：从双端队列尾部删除一个元素。如果操作成功返回 true ，否则返回 false 。

int getFront() )：从双端队列头部获得一个元素。如果双端队列为空，返回 -1 。

int getRear() ：获得双端队列的最后一个元素。如果双端队列为空，返回 -1 。

boolean isEmpty() ：若双端队列为空，则返回 true ，否则返回 false 。

boolean isFull() ：若双端队列满了，则返回 true ，否则返回 false 。

思路

这道题思路类似 622 题，无非是把普通的 queue 变成 dequeue。做这道题之前可以先做一些相关题目。

复杂度

时间O(n)
空间O(n)

代码

Java实现

class Node {
    int value;
    Node prev;
    Node next;
    public Node(int value) {
        this.value = value;
    }
}

class MyCircularDeque {
    int size;
    int k;
    Node head;
    Node tail;

    public MyCircularDeque(int k) {
        this.size = 0;
        this.k = k;
        head = new Node(-1);
        tail = new Node(-1);
        head.next = tail;
        tail.prev = head;
    }
    
    public boolean insertFront(int value) {
        if (isFull()) {
            return false;
        }
        Node newNode = new Node(value);
        newNode.next = head.next;
        newNode.prev = head;
        head.next.prev = newNode;
        head.next = newNode;
        size++;
        return true;
    }
    
    public boolean insertLast(int value) {
        if (isFull()) {
            return false;
        }
        Node newNode = new Node(value);
        newNode.next = tail;
        newNode.prev = tail.prev;
        tail.prev.next = newNode;
        tail.prev = newNode;
        size++;
        return true;
    }
    
    public boolean deleteFront() {
        if (isEmpty()) {
            return false;
        }
        head.next.next.prev = head;
        head.next = head.next.next;
        size--;
        return true;
    }
    
    public boolean deleteLast() {
        if (isEmpty()) {
            return false;
        }
        tail.prev.prev.next = tail;
        tail.prev = tail.prev.prev;
        size--;
        return true;
    }
    
    public int getFront() {
        return head.next.value;
    }
    
    public int getRear() {
        return tail.prev.value;
    }
    
    public boolean isEmpty() {
        return size == 0;
    }
    
    public boolean isFull() {
        return size == k;
    }
}

/**
 * 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();
 */