leetcode-641-Design-Circular-Deque

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描述

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

Your implementation should support following operations:

  • MyCircularDeque(k): Constructor, set the size of the deque to be k.
  • insertFront(): Adds an item at the front of Deque. Return true if the operation is successful.
  • insertLast(): Adds an item at the rear of Deque. Return true if the operation is successful.
  • deleteFront(): Deletes an item from the front of Deque. Return true if the operation is successful.
  • deleteLast(): Deletes an item from the rear of Deque. Return true if the operation is successful.
  • getFront(): Gets the front item from the Deque. If the deque is empty, return -1.
  • getRear(): Gets the last item from Deque. If the deque is empty, return -1.
  • isEmpty(): Checks whether Deque is empty or not.
  • isFull(): Checks whether Deque is full or not.

Example:

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MyCircularDeque circularDeque = new MycircularDeque(3); // set the size to be 3
circularDeque.insertLast(1);			// return true
circularDeque.insertLast(2);			// return true
circularDeque.insertFront(3);			// return true
circularDeque.insertFront(4);			// return false, the queue is full
circularDeque.getRear();  			// return 2
circularDeque.isFull();				// return true
circularDeque.deleteLast();			// return true
circularDeque.insertFront(4);			// return true
circularDeque.getFront();			// 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 Deque library.

分析

实现双向队列的常用接口，这道题可以当做很多链表类问题的模板。题目里虽然要求环形，实际上实现对应接口就行了，不一定非得是环形。

类似的问题还有：622. Design Circular Queue，那道题只需要实现单向的先进先出队列。

解决方案1(Java)

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class MyCircularDeque {
    Node head, rear;
    int size, k;

    /** Initialize your data structure here. Set the size of the deque to be k. */
    public MyCircularDeque(int k) {
        this.head = new Node(-1);
        this.rear = head;
        this.size = 0;
        this.k = k;
    }
    
    /** Adds an item at the front of Deque. Return true if the operation is successful. */
    public boolean insertFront(int value) {
        if (isFull()) {
            return false;
        }
        Node toInsert = new Node(value);
        toInsert.next = head.next;
        this.head.next = toInsert;
        toInsert.pre = head;
        if (toInsert.next == null) {
            this.rear = toInsert;
        } else {
            toInsert.next.pre = toInsert;
        }
        this.size++;
        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;
        }
        Node toInsert = new Node(value);
        toInsert.pre = rear;
        this.rear.next = toInsert;
        this.rear = toInsert;
        this.size++;
        return true;
    }
    
    /** Deletes an item from the front of Deque. Return true if the operation is successful. */
    public boolean deleteFront() {
        if (isEmpty()) {
            return false;
        }
        Node toDelete = head.next;
        this.head.next = toDelete.next;
        if (toDelete == rear) {
            this.rear = head;
        } else {
            toDelete.next.pre = head;
        }
        toDelete.next = null;
        toDelete.pre = null;
        this.size--;
        return true;
    }
    
    /** Deletes an item from the rear of Deque. Return true if the operation is successful. */
    public boolean deleteLast() {
        if (isEmpty()) {
            return false;
        }
        Node toDeletePre = rear.pre;
        toDeletePre.next = null;
        if (toDeletePre == head) {
            this.rear = head;
        } else {
            this.rear = toDeletePre;
        }
        this.size--;
        return true;
    }
    
    /** Get the front item from the deque. */
    public int getFront() {
        return isEmpty() ? -1 : this.head.next.value;
    }
    
    /** Get the last item from the deque. */
    public int getRear() {
        return isEmpty() ? -1 : this.rear.value;
    }
    
    /** Checks whether the circular deque is empty or not. */
    public boolean isEmpty() {
        return this.size == 0;
    }
    
    /** Checks whether the circular deque is full or not. */
    public boolean isFull() {
        return this.size >= this.k;
    }
}

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

/**
 * 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();
 */

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