Leetcode: Design Circular Queue

Posted on July 21, 2018September 23, 2019 by braindenny

Design Circular Queue

Similar Problems:

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

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 Queue library.

Github: code.dennyzhang.com

Credits To: leetcode.com

Leave me comments, if you have better ways to solve.

Solution:

// https://code.dennyzhang.com/design-circular-queue
// Basic Ideas: Use an Array
// Differentiate two cases: full or empty
// Two pointers: front, rear
//     The cell of rear won't store any items.
//     When rear == front -> empty
//     When (rear+1)%n == front -> full
// Complexity: Time O(1), Space O(n)
type MyCircularQueue struct {
    l []int
    front, rear, size int
}


/** Initialize your data structure here. Set the size of the queue to be k. */
func Constructor(k int) MyCircularQueue {
    queue := MyCircularQueue{}
    queue.l = make([]int, k+1)
    queue.front, queue.rear, queue.size = 0, 0, k+1
    return queue
}

/** Insert an element into the circular queue. Return true if the operation is successful. */
func (this *MyCircularQueue) EnQueue(value int) bool {
    if this.IsFull() { return false }
    this.l[this.rear] = value
    this.rear = (this.rear+1) % this.size
    return true
}


/** Delete an element from the circular queue. Return true if the operation is successful. */
func (this *MyCircularQueue) DeQueue() bool {
    if this.IsEmpty() { return false }
    this.front = (this.front+1+this.size) % this.size
    return true
}


/** Get the front item from the queue. */
func (this *MyCircularQueue) Front() int {
    if this.IsEmpty() { return -1 }
    return this.l[this.front]
}


/** Get the last item from the queue. */
func (this *MyCircularQueue) Rear() int {
    if this.IsEmpty() { return -1 }
    return this.l[(this.rear-1+this.size) % this.size]
}


/** Checks whether the circular queue is empty or not. */
func (this *MyCircularQueue) IsEmpty() bool {
    return this.rear == this.front
}


/** Checks whether the circular queue is full or not. */
func (this *MyCircularQueue) IsFull() bool {
    return (this.rear+1) % this.size == this.front
}


/**
 * Your MyCircularQueue object will be instantiated and called as such:
 * obj := Constructor(k);
 * param_1 := obj.EnQueue(value);
 * param_2 := obj.DeQueue();
 * param_3 := obj.Front();
 * param_4 := obj.Rear();
 * param_5 := obj.IsEmpty();
 * param_6 := obj.IsFull();
 */

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