设计循环双端队列


情到浓时终转凉″ 提交于 2020-01-14 23:08:01

题目:
设计实现双端队列。
你的实现需要支持以下操作:

MyCircularDeque(k):构造函数,双端队列的大小为k。
insertFront():将一个元素添加到双端队列头部。 如果操作成功返回 true。
insertLast():将一个元素添加到双端队列尾部。如果操作成功返回 true。
deleteFront():从双端队列头部删除一个元素。 如果操作成功返回 true。
deleteLast():从双端队列尾部删除一个元素。如果操作成功返回 true。
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。
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。
isEmpty():检查双端队列是否为空。
isFull():检查双端队列是否满了。

方法一:数组实现

class MyCircularDeque {
    int[]a;
    int size=0;
    /** Initialize your data structure here. Set the size of the deque to be k. */
    public MyCircularDeque(int k) {
        a=new int[k];
    }
    
    /** Adds an item at the front of Deque. Return true if the operation is successful. */
    public boolean insertFront(int value) {
        if(this.isFull()){
            return false;
        }
        for(int i=this.size;i>0;i--){
            a[i]=a[i-1];
        }
        a[0]=value;
        size++;
        return true;
    }
    
    /** Adds an item at the rear of Deque. Return true if the operation is successful. */
    public boolean insertLast(int value) {
        if(this.isFull()){
            return false;
        }
        a[size++]=value;
        return true;

    }
    
    /** Deletes an item from the front of Deque. Return true if the operation is successful. */
    public boolean deleteFront() {
        if(this.isEmpty()){
            return false;
        }
        for(int i=1;i<size;i++){
            a[i-1]=a[i];
        }
        size--;
        return true;
    }
    
    /** Deletes an item from the rear of Deque. Return true if the operation is successful. */
    public boolean deleteLast() {
        if(this.isEmpty()){
            return false;
        }
        size--;
        return true;
    }
    
    /** Get the front item from the deque. */
    public int getFront() {
        if(this.isEmpty()){
            return -1;
        }
        return a[0];
    }
    
    /** Get the last item from the deque. */
    public int getRear() {
        if(this.isEmpty()){
            return -1;
        }
        return a[size-1];
    }
    
    /** Checks whether the circular deque is empty or not. */
    public boolean isEmpty() {
        if(this.size==0){
            return true;
        }
        return false;
    }
    
    /** Checks whether the circular deque is full or not. */
    public boolean isFull() {
        if(a.length==size){
            return true;
        }
        return false;
    }
}

方法二:循环数组

public class MyCircularDeque {
    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];
        front = 0;
        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(){
        return (rear + 1) % capacity == front;
    }
}

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