Queue

IsFull

What is the isFull Operation?

isFull only matters for queues with a hard capacity limit, like array-backed ones. It tells you true when there's no room left for another enqueue, and false when there's still space: a guard that stops you from writing past the end of the underlying array.

How Does It Work?

The isFull operation examines the queue's capacity and current state.

Example scenarios (for a queue with capacity 3):

  1. Full Queue: [10, 20, 30]
    • isFull() → returns true
  2. Non-full Queue: [10, 20]
    • isFull() → returns false

Note: Dynamic implementations (like linked lists) typically don't need this operation as they can grow indefinitely.

Implementation Details

Different approaches to check if a queue is full:

  1. Linear Array Implementation:
    • Check if rear == capacity - 1
    • Simple but wastes space when front ≠ 0
  2. Circular Array Implementation:
    • Check if (rear + 1) % capacity == front
    • More space-efficient
  3. Size Counter Approach:
    • Maintain a size variable
    • Check if size == capacity

Algorithm Steps

For circular array implementation:

  1. Calculate next rear position: (rear + 1) % capacity
  2. Compare with front position
  3. If equal, return true (queue is full)
  4. Else return false (space available)

Time Complexity

The isFull operation always runs in O(1) constant time because:

  • It only requires simple pointer arithmetic and comparison
  • No iteration through elements is needed
  • Performance is independent of queue size

Practical Usage

isFull is essential in:

  • Bounded buffer problems
  • Producer-consumer scenarios
  • Memory-constrained systems
  • Before enqueue operations to prevent overflow

The isFull operation is critical for robust queue implementations in fixed-capacity scenarios, ensuring data integrity by preventing buffer overflow conditions in system programming and embedded applications.

Daily DSA Challenge by Scale Engineer

Visualise isFull operation in real-time

Queue is empty

Test Your Knowledge before moving forward!

Queue isFull Operation Quiz

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  • +1 point for each correct answer
  • 0 points for wrong answers
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  • Earn stars based on your final score (max 5 stars)

Queue IsFull Operation

// Array Queue isFull in JavaScript
class ArrayQueue {
  constructor(capacity) {
    this.arr = new Array(capacity);
    this.front = -1;
    this.rear = -1;
    this.capacity = capacity;
  }

  isFull() {
    return (this.rear + 1) % this.capacity === this.front;
  }
}

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Explore Other Operations

Peek Front

Enqueue & Dequeue

Is Empty