641. Design Circular Deque

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:

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.

class MyCircularDeque {
    LinkedList<Integer> list;
    int len = 0;
    int le = 0;
    /** Initialize your data structure here. Set the size of the deque to be k. */
    public MyCircularDeque(int k) {
        list = new LinkedList<Integer>();
        le = k;
    }
    
    /** Adds an item at the front of Deque. Return true if the operation is successful. */
    public boolean insertFront(int value) {
        if(!isFull()) {
            list.addFirst(value);
            len++;
            return true;
        }
        else return false;
    }
    
    /** Adds an item at the rear of Deque. Return true if the operation is successful. */
    public boolean insertLast(int value) {
        if(!isFull()) {
            list.addLast(value);
            len++;
            return true;
        }
        else return false;
    }
    
    /** Deletes an item from the front of Deque. Return true if the operation is successful. */
    public boolean deleteFront() {
        if(!isEmpty()){
            list.removeFirst();
            len--;
            return true;
        }
        return false;
    }
    
    /** Deletes an item from the rear of Deque. Return true if the operation is successful. */
    public boolean deleteLast() {
        if(!isEmpty()){
            list.removeLast();
            len--;
            return true;
        }
        return false;
    }
    
    /** Get the front item from the deque. */
    public int getFront() {
        if(isEmpty()) return -1;
        return list.peekFirst();
    }
    
    /** Get the last item from the deque. */
    public int getRear() {
        if(isEmpty()) return -1;
        return list.peekLast();
    }
    
    /** Checks whether the circular deque is empty or not. */
    public boolean isEmpty() {
        return len == 0;
    }
    
    /** Checks whether the circular deque is full or not. */
    public boolean isFull() {
        return len == le;
    }
}

/**
 * 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();
 */

啊这，

java的linkedlist和arraydequeue好像，都能offer/addFrist/Last，remove/poll/peekFirst/Last，用起来就很方便

用来设计这种dequeue就很方便

class MyCircularDeque {

    int[] queue;
    int front, tail;
    int count;
    
    /** Initialize your data structure here. Set the size of the deque to be k. */
    public MyCircularDeque(int k) {
        queue = new int[k];
        front = 0;
        tail = 0;
        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;
        }
        front = (front - 1 + queue.length) % queue.length;
        if (isEmpty()) {
            tail = front;
        }
        queue[front] = value;
        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;
        }
        tail = (tail + 1) % queue.length;
        if (isEmpty()) {
            front = tail;
        }
        queue[tail] = value;
        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 + 1) % queue.length;
        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;
        }
        tail = (tail - 1 + queue.length) % queue.length;
        count--;
        return true;
    }
    
    /** Get the front item from the deque. */
    public int getFront() {
        return isEmpty() ? -1 : queue[front];
    }
    
    /** Get the last item from the deque. */
    public int getRear() {
        return isEmpty() ? -1 : queue[tail];
    }
    
    /** 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 == queue.length;
    }
}

我是啥b，不能用已有的collection的

用array，add的时候先算下一个head/tail位置，如果此时变空，就让两个相等，因为要重新开始

addFirst就是（head-1+k）%k

addLast就是（tail+1）%k