Design Circular Queue 25 XP Medium

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A Circular Queue uses a fixed-size array where the end wraps around to the beginning. When the queue is full, you can't add more — but when an element is removed from the front, that space becomes available at the end.

cq = MyCircularQueue(3)  # capacity 3
cq.enQueue(1)  # True   [1, _, _]
cq.enQueue(2)  # True   [1, 2, _]
cq.enQueue(3)  # True   [1, 2, 3] — full!
cq.enQueue(4)  # False  — can't add, it's full
cq.Rear()      # 3
cq.isFull()    # True
cq.deQueue()   # True   [_, 2, 3]
cq.enQueue(4)  # True   [4, 2, 3] — wraps around!

Key idea: Use two pointers — head and tail — with modular arithmetic:

head: Index of front element
tail: Index where next enqueue goes
Wrap around: (index + 1) % capacity
Track count to distinguish full vs empty

📋 Instructions

Implement a circular queue with the given operations. Test the enQueue, deQueue, Front, Rear, isEmpty, and isFull operations.

Use a list of fixed size, head pointer, and count. enQueue: place at (head+count)%k, increment count. deQueue: increment head = (head+1)%k, decrement count. Front: data[head]. Rear: data[(head+count-1)%k].

🧪 Test Cases

Input

cq.enQueue(1)

Expected

True

Boolean check

Input

cq.enQueue(2)

Expected

True

Boolean check

Input

cq.enQueue(3)

Expected

True

Boolean check

Input

cq.enQueue(4)

Expected

False

Boolean check

Input

cq.Rear()

Expected

3

Test case 5

Input

cq.isFull()

Expected

True

Boolean check

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main.py

Hi! I'm Rex 👋

class MyCircularQueue:
    def __init__(self, k):
        self.data = [0] * k
        self.head = 0
        self.count = 0
        self.capacity = k
    
    def enQueue(self, value):
        if self.isFull():
            return False
        idx = (self.head + self.count) % self.capacity
        self.data[idx] = value
        self.count += 1
        return True
    
    def deQueue(self):
        if self.isEmpty():
            return False
        self.head = (self.head + 1) % self.capacity
        self.count -= 1
        return True
    
    def Front(self):
        if self.isEmpty():
            return -1
        return self.data[self.head]
    
    def Rear(self):
        if self.isEmpty():
            return -1
        # Return the last element
        pass
    
    def isEmpty(self):
        return self.count == 0
    
    def isFull(self):
        return self.count == self.capacity

cq = MyCircularQueue(3)
print(cq.enQueue(1))
print(cq.enQueue(2))
print(cq.enQueue(3))
print(cq.enQueue(4))
print(cq.Rear())
print(cq.isFull())
print(cq.deQueue())
print(cq.enQueue(4))
print(cq.Rear())

Output

Ready. Press ▶ Run or Ctrl+Enter.

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