算法记录

LeetCode 题目：

  设计实现双端队列。

说明

一、题目

  实现相关的方法。

二、分析

• 可用双向链表进行求解，也可用循环队列进行存储。

class Node{
    Integer value;
    Node first;
    Node last;
    public Node(int val) {
        value = val;
        first = null;
        last = null;
    }
}

class MyCircularDeque {
    private Integer size;
    private Integer count;
    private Node front;
    private Node rear;
    /** Initialize your data structure here. Set the size of the deque to be k. */
    public MyCircularDeque(int k) {
        size = k;
        count = 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;
        Node temp = new Node(value);
        if(isEmpty()) {
            front = rear = temp;;
        } else {
            temp.last = front;
            front.first = temp;
            front = front.first;
        }   
        count++;
        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 temp = new Node(value);
        if(isEmpty()) {
            front = rear = temp;
        } else {
            rear.last = temp;
            temp.first = rear;
            rear = rear.last;
        }
        count++;
        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 = front.last;
        count--;
        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 = rear.first;
        count--;
        return true;
    }
    
    /** Get the front item from the deque. */
    public int getFront() {
        if(isEmpty()) return -1;
        return front.value;
    }
    
    /** Get the last item from the deque. */
    public int getRear() {
        if(isEmpty()) return -1;
        return rear.value;
    }
    
    /** Checks whether the circular deque is empty or not. */
    public boolean isEmpty() {
        return count == 0;
    }
    
    /** Checks whether the circular deque is full or not. */
    public boolean isFull() {
        return count == size;
    }
}

总结

熟悉队列的存储性质。