Question

622. Design Circular Queue

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Description

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.

Implement the MyCircularQueue class:

• MyCircularQueue(k) Initializes the object with the size of the queue to be k.
• int Front() Gets the front item from the queue. If the queue is empty, return -1.
• int Rear() Gets the last item from the queue. If the queue is empty, return -1.
• boolean enQueue(int value) Inserts an element into the circular queue. Return true if the operation is successful.
• boolean deQueue() Deletes an element from the circular queue. Return true if the operation is successful.
• boolean isEmpty() Checks whether the circular queue is empty or not.
• boolean isFull() Checks whether the circular queue is full or not.

You must solve the problem without using the built-in queue data structure in your programming language. 

 

Example 1:

Input
["MyCircularQueue", "enQueue", "enQueue", "enQueue", "enQueue", "Rear", "isFull", "deQueue", "enQueue", "Rear"]
[[3], [1], [2], [3], [4], [], [], [], [4], []]
Output
[null, true, true, true, false, 3, true, true, true, 4]

Explanation
MyCircularQueue myCircularQueue = new MyCircularQueue(3);
myCircularQueue.enQueue(1); // return True
myCircularQueue.enQueue(2); // return True
myCircularQueue.enQueue(3); // return True
myCircularQueue.enQueue(4); // return False
myCircularQueue.Rear();   // return 3
myCircularQueue.isFull();   // return True
myCircularQueue.deQueue();  // return True
myCircularQueue.enQueue(4); // return True
myCircularQueue.Rear();   // return 4

 

Constraints:

• 1 <= k <= 1000
• 0 <= value <= 1000
• At most 3000 calls will be made to enQueue, deQueue, Front, Rear, isEmpty, and isFull.

Solutions

Solution 1

class MyCircularQueue:
  def __init__(self, k: int):
    self.q = [0] * k
    self.front = 0
    self.size = 0
    self.capacity = k

  def enQueue(self, value: int) -> bool:
    if self.isFull():
      return False
    idx = (self.front + self.size) % self.capacity
    self.q[idx] = value
    self.size += 1
    return True

  def deQueue(self) -> bool:
    if self.isEmpty():
      return False
    self.front = (self.front + 1) % self.capacity
    self.size -= 1
    return True

  def Front(self) -> int:
    return -1 if self.isEmpty() else self.q[self.front]

  def Rear(self) -> int:
    if self.isEmpty():
      return -1
    idx = (self.front + self.size - 1) % self.capacity
    return self.q[idx]

  def isEmpty(self) -> bool:
    return self.size == 0

  def isFull(self) -> bool:
    return self.size == self.capacity


# Your MyCircularQueue object will be instantiated and called as such:
# obj = MyCircularQueue(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()

class MyCircularQueue {
  private int[] q;
  private int front;
  private int size;
  private int capacity;

  public MyCircularQueue(int k) {
    q = new int[k];
    capacity = k;
  }

  public boolean enQueue(int value) {
    if (isFull()) {
      return false;
    }
    int idx = (front + size) % capacity;
    q[idx] = value;
    ++size;
    return true;
  }

  public boolean deQueue() {
    if (isEmpty()) {
      return false;
    }
    front = (front + 1) % capacity;
    --size;
    return true;
  }

  public int Front() {
    if (isEmpty()) {
      return -1;
    }
    return q[front];
  }

  public int Rear() {
    if (isEmpty()) {
      return -1;
    }
    int idx = (front + size - 1) % capacity;
    return q[idx];
  }

  public boolean isEmpty() {
    return size == 0;
  }

  public boolean isFull() {
    return size == capacity;
  }
}

/**
 * Your MyCircularQueue object will be instantiated and called as such:
 * MyCircularQueue obj = new MyCircularQueue(k);
 * boolean param_1 = obj.enQueue(value);
 * boolean param_2 = obj.deQueue();
 * int param_3 = obj.Front();
 * int param_4 = obj.Rear();
 * boolean param_5 = obj.isEmpty();
 * boolean param_6 = obj.isFull();
 */

class MyCircularQueue {
private:
  int front;
  int size;
  int capacity;
  vector<int> q;

public:
  MyCircularQueue(int k) {
    capacity = k;
    q = vector<int>(k);
    front = size = 0;
  }

  bool enQueue(int value) {
    if (isFull()) return false;
    int idx = (front + size) % capacity;
    q[idx] = value;
    ++size;
    return true;
  }

  bool deQueue() {
    if (isEmpty()) return false;
    front = (front + 1) % capacity;
    --size;
    return true;
  }

  int Front() {
    if (isEmpty()) return -1;
    return q[front];
  }

  int Rear() {
    if (isEmpty()) return -1;
    int idx = (front + size - 1) % capacity;
    return q[idx];
  }

  bool isEmpty() {
    return size == 0;
  }

  bool isFull() {
    return size == capacity;
  }
};

/**
 * Your MyCircularQueue object will be instantiated and called as such:
 * MyCircularQueue* obj = new MyCircularQueue(k);
 * bool param_1 = obj->enQueue(value);
 * bool param_2 = obj->deQueue();
 * int param_3 = obj->Front();
 * int param_4 = obj->Rear();
 * bool param_5 = obj->isEmpty();
 * bool param_6 = obj->isFull();
 */

type MyCircularQueue struct {
  front  int
  size   int
  capacity int
  q    []int
}

func Constructor(k int) MyCircularQueue {
  q := make([]int, k)
  return MyCircularQueue{0, 0, k, q}
}

func (this *MyCircularQueue) EnQueue(value int) bool {
  if this.IsFull() {
    return false
  }
  idx := (this.front + this.size) % this.capacity
  this.q[idx] = value
  this.size++
  return true
}

func (this *MyCircularQueue) DeQueue() bool {
  if this.IsEmpty() {
    return false
  }
  this.front = (this.front + 1) % this.capacity
  this.size--
  return true
}

func (this *MyCircularQueue) Front() int {
  if this.IsEmpty() {
    return -1
  }
  return this.q[this.front]
}

func (this *MyCircularQueue) Rear() int {
  if this.IsEmpty() {
    return -1
  }
  idx := (this.front + this.size - 1) % this.capacity
  return this.q[idx]
}

func (this *MyCircularQueue) IsEmpty() bool {
  return this.size == 0
}

func (this *MyCircularQueue) IsFull() bool {
  return this.size == this.capacity
}

/**
 * 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();
 */

class MyCircularQueue {
  private queue: number[];
  private left: number;
  private right: number;
  private capacity: number;

  constructor(k: number) {
    this.queue = new Array(k);
    this.left = 0;
    this.right = 0;
    this.capacity = k;
  }

  enQueue(value: number): boolean {
    if (this.isFull()) {
      return false;
    }
    this.queue[this.right % this.capacity] = value;
    this.right++;
    return true;
  }

  deQueue(): boolean {
    if (this.isEmpty()) {
      return false;
    }
    this.left++;
    return true;
  }

  Front(): number {
    if (this.isEmpty()) {
      return -1;
    }
    return this.queue[this.left % this.capacity];
  }

  Rear(): number {
    if (this.isEmpty()) {
      return -1;
    }
    return this.queue[(this.right - 1) % this.capacity];
  }

  isEmpty(): boolean {
    return this.right - this.left === 0;
  }

  isFull(): boolean {
    return this.right - this.left === this.capacity;
  }
}

/**
 * Your MyCircularQueue object will be instantiated and called as such:
 * var obj = new MyCircularQueue(k)
 * var param_1 = obj.enQueue(value)
 * var param_2 = obj.deQueue()
 * var param_3 = obj.Front()
 * var param_4 = obj.Rear()
 * var param_5 = obj.isEmpty()
 * var param_6 = obj.isFull()
 */

struct MyCircularQueue {
  queue: Vec<i32>,
  left: usize,
  right: usize,
  capacity: usize,
}

/**
 * `&self` means the method takes an immutable reference.
 * If you need a mutable reference, change it to `&mut self` instead.
 */
impl MyCircularQueue {
  fn new(k: i32) -> Self {
    let k = k as usize;
    Self {
      queue: vec![0; k],
      left: 0,
      right: 0,
      capacity: k,
    }
  }

  fn en_queue(&mut self, value: i32) -> bool {
    if self.is_full() {
      return false;
    }
    self.queue[self.right % self.capacity] = value;
    self.right += 1;
    true
  }

  fn de_queue(&mut self) -> bool {
    if self.is_empty() {
      return false;
    }
    self.left += 1;
    true
  }

  fn front(&self) -> i32 {
    if self.is_empty() {
      return -1;
    }
    self.queue[self.left % self.capacity]
  }

  fn rear(&self) -> i32 {
    if self.is_empty() {
      return -1;
    }
    self.queue[(self.right - 1) % self.capacity]
  }

  fn is_empty(&self) -> bool {
    self.right - self.left == 0
  }

  fn is_full(&self) -> bool {
    self.right - self.left == self.capacity
  }
}/**
 * Your MyCircularQueue object will be instantiated and called as such:
 * let obj = MyCircularQueue::new(k);
 * let ret_1: bool = obj.en_queue(value);
 * let ret_2: bool = obj.de_queue();
 * let ret_3: i32 = obj.front();
 * let ret_4: i32 = obj.rear();
 * let ret_5: bool = obj.is_empty();
 * let ret_6: bool = obj.is_full();
 */