Design Circular Queue LeetCode Solution

Problem – Design Circular Queue

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.

Implementation 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.

Design Circular Queue LeetCode Solution in Python

class MyCircularQueue:
    def __init__(self, k: int):
        self.data = [0] * k
        self.maxSize = k
        self.head = 0
        self.tail = -1
    def enQueue(self, val: int) -> bool:
        if self.isFull(): return False
        self.tail = (self.tail + 1) % self.maxSize
        self.data[self.tail] = val
        return True
    def deQueue(self) -> bool:
        if self.isEmpty(): return False
        if self.head == self.tail: self.head, self.tail = 0, -1
        else: self.head = (self.head + 1) % self.maxSize
        return True
    def Front(self) -> int:
        return -1 if self.isEmpty() else self.data[self.head]
    def Rear(self) -> int:
        return -1 if self.isEmpty() else self.data[self.tail]
    def isEmpty(self) -> bool:
        return self.tail == -1
    def isFull(self) -> bool:
        return not self.isEmpty() and (self.tail + 1) % self.maxSize == self.head

Design Circular Queue LeetCode Solution in Java

class MyCircularQueue {
    int maxSize, head = 0, tail = -1;
    int[] data;
    public MyCircularQueue(int k) {
        data = new int[k];
        maxSize = k;
    }
    public boolean enQueue(int val) {
        if (isFull()) return false;
        tail = (tail + 1) % maxSize;
        data[tail] = val;
        return true;
    }
    public boolean deQueue() {
        if (isEmpty()) return false;
        if (head == tail) {
            head = 0;
            tail = -1;
        } else head = (head + 1) % maxSize;
        return true;
    }
    public int Front() {
        return isEmpty() ? -1 : data[head];
    }
    public int Rear() {
        return isEmpty() ? -1 : data[tail];
    }
    public boolean isEmpty() {
        return tail == -1;
    }
    public boolean isFull() {
        return !isEmpty() && (tail + 1) % maxSize == head;
    }

Design Circular Queue LeetCode Solution in C++

class MyCircularQueue {
public:
    MyCircularQueue(int k) {
        data.resize(k);
        maxSize = k;
    }
    bool enQueue(int val) {
        if (isFull()) return false;
        tail = (tail + 1) % maxSize;
        data[tail] = val;
        return true;
    }
    bool deQueue() {
        if (isEmpty()) return false;
        if (head == tail) head = 0, tail = -1;
        else head = (head + 1) % maxSize;
        return true;
    }
    int Front() {
        return isEmpty() ? -1 : data[head];
    }
    int Rear() {
        return isEmpty() ? -1 : data[tail];
    }
    bool isEmpty() {
        return tail == -1;
    }
    bool isFull() {
        return !isEmpty() && (tail + 1) % maxSize == head;
    }
private:
    int maxSize, head = 0, tail = -1;
    vector<int> data;
};

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