Lintcode 955. Implement Queue by Circular Array

Implement queue by circulant array. You need to support the following methods:

1. CircularQueue(n): initialize a circular array with size n to store elements
2. boolean isFull(): return true if the array is full
3. boolean isEmpty(): return true if there is no element in the array
4. void enqueue(element): add an element to the queue
5. int dequeue(): pop an element from the queue

Example

Example 1:

Input:
CircularQueue(5)
isFull()
isEmpty()
enqueue(1)
enqueue(2)
dequeue()
Output:
["false","true","1"]

Example 2:

Input:
CircularQueue(5)
isFull()
isEmpty()
enqueue(1)
enqueue(2)
dequeue()
dequeue()
enqueue(1)
enqueue(2)
enqueue(3)
enqueue(4)
enqueue(5)
isFull()
dequeue()
dequeue()
dequeue()
dequeue()
dequeue()
Output:
["false","true","1","2","true","1","2","3","4","5"]

Notice

it's guaranteed in the test cases we won't call enqueue if it's full and we also won't call dequeue if it's empty. So it's ok to raise exception in scenarios described above.

Code (Java):

public class CircularQueue {
    private int front; // index for dequeue
    private int rear; // index for enqueue
    private int[] array;
    private int size; // number of elements in the array
    
    public CircularQueue(int n) {
        // initialize your data structure here
        array = new int[n];
        front = 0;
        rear = 0;
        size = 0;
    }
    /**
     * @return:  return true if the array is full
     */
    public boolean isFull() {
        // write your code here
        return size >= array.length;
    }

    /**
     * @return: return true if there is no element in the array
     */
    public boolean isEmpty() {
        // write your code here
        return size == 0;
    }

    /**
     * @param element: the element given to be added
     * @return: nothing
     */
    public void enqueue(int element) {
        // write your code here
        rear = (front + size) % array.length;
        array[rear] = element;
        size += 1;
    }

    /**
     * @return: pop an element from the queue
     */
    public int dequeue() {
        // write your code here
        int ans = array[front];
        front = (front + 1) % array.length;
        size -= 1;
        return ans;
    }
}