622. Design Circular Queue

Design Circular Queue


https://leetcode.com/problems/design-circular-queue/discuss/149420/Concise-Java-using-array/167623

https://www.youtube.com/watch?v=Ig34WPrgofI




dequeue doesn’t change the value at the top, it just moves the front pointer to the next one , and len - -.

还是不太明白， 走个例子

Enqueue, dequeue 和 queue 中 的 push(), pop() 一样的 

class MyCircularQueue {
    // leave the global var here so they are be accessed from all public classes
    int[] a;
    int front, rear = -1; // idk why set -1
    int len = 0;

    /** Initialize your data structure here. Set the size of the queue to be k. */
    public MyCircularQueue(int k) {
        a = new int[k];
        
        
    }
    
    /** Insert an element into the circular queue. Return true if the operation is successful. */
    public boolean enQueue(int value) {
        if(!isFull()){
            len++;
            rear = (rear + 1) % a.length;// so when rear index is 2, and array is not full, we can move to index 0
            a[rear] = value;
            return true;
        }else{
            return false;
        }
    }
    
    /** Delete an element from the circular queue. Return true if the operation is successful. */
    public boolean deQueue() {
        if(!isEmpty()){
            // deque , move front pointer to the next one, don't actually delete the val
            front = (front + 1) % a.length;// not sure why % 
            len--;
            return true;
        }else{
            return false;
        }
        
    }
    
    /** Get the front item from the queue. */
    public int Front() {
        if(isEmpty()){
            return -1;
        }else{
            return a[front];
        }
        
    }
    
    /** Get the last item from the queue. */
    public int Rear() {
        if(isEmpty()){
            return -1;
        }else{
            return a[rear];
        }
        
    }
    
    /** Checks whether the circular queue is empty or not. */
    public boolean isEmpty() {
        return len == 0;
        
    }
    
    /** Checks whether the circular queue is full or not. */
    public boolean isFull() {
        return len == a.length;
        // try return len == k;
        
    }
}

 

Design your implementation of the circular queue. The circular queue is a linear data structure in which the operations are performed based on FIFO (First In First Out) principle and the last position is connected back to the first position to make a circle. It is also called "Ring Buffer".

One of the benefits of the circular queue is that we can make use of the spaces in front of the queue. In a normal queue, once the queue becomes full, we cannot insert the next element even if there is a space in front of the queue. But using the circular queue, we can use the space to store new values.

Your implementation should support following operations:

• MyCircularQueue(k): Constructor, set the size of the queue to be k.
• Front: Get the front item from the queue. If the queue is empty, return -1.
• Rear: Get the last item from the queue. If the queue is empty, return -1.
• enQueue(value): Insert an element into the circular queue. Return true if the operation is successful.
• deQueue(): Delete an element from the circular queue. Return true if the operation is successful.
• isEmpty(): Checks whether the circular queue is empty or not.
• isFull(): Checks whether the circular queue is full or not.

 

Example:

MyCircularQueue circularQueue = new MycircularQueue(3); // set the size to be 3
circularQueue.enQueue(1);  // return true
circularQueue.enQueue(2);  // return true
circularQueue.enQueue(3);  // return true
circularQueue.enQueue(4);  // return false, the queue is full
circularQueue.Rear();  // return 3
circularQueue.isFull();  // return true
circularQueue.deQueue();  // return true
circularQueue.enQueue(4);  // return true
circularQueue.Rear();  // return 4