QueueUsingArray.java

package gfg.ds.queue;

import gfg.ds.queue.adt.Queue;

/** NOTE: If we use another variable 'size' then checking overflow becomes easy. */
public class QueueUsingArray implements Queue {
  protected int values[];
  int front;
  int rear;

  QueueUsingArray(int size) {
    values = new int[size];
    front = -1;
    rear = 0;
  }

  /** t=O(1) */
  @Override
  public QueueUsingArray enqueue(int data) {
    assert !isFull() : "Queue is full";
    if (front == -1) {
      front = 0;
    }
    values[rear++] = data;
    rear = (rear) % values.length;
    return this;
  }

  /** t=O(1) */
  @Override
  public int dequeue() {
    assert !isEmpty() : "Queue is empty";
    int temp = values[front];
    front = (front + 1) % values.length;
    if (front == rear) {
      front = -1;
      rear = 0;
    }
    return temp;
  }

  /** t=O(1) */
  @Override
  public int front() {
    assert !isEmpty() : "Queue is empty";
    return values[front];
  }

  /** t=O(1) */
  @Override
  public int rear() {
    assert !isEmpty() : "Queue is empty";
    if (rear == 0) {
      return values[values.length - 1];
    }
    return values[rear - 1];
  }

  /** @return true if queue is full */
  public boolean isFull() {
    return front == rear;
  }

  /** @return true if queue is empty */
  public boolean isEmpty() {
    return front == -1;
  }

  public String toString() {
    if (isEmpty()) {
      return "{}";
    }
    StringBuilder sb = new StringBuilder();
    sb.append("{");
    int tempFront = front;
    int tempRear = rear;
    do {
      sb.append(values[tempFront]).append(",");
      tempFront = (tempFront + 1) % values.length;
    } while (tempFront != tempRear);
    sb.append("}").append("front:").append(front).append(",rear:").append(rear);
    return sb.toString();
  }
}