Circular Queue

Posted: 14 Feb, 2021
Difficulty: Easy


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You will be given ‘Q’ queries. You need to implement a circular queue according to those queries. Each query will belong to one of these two types:

1 ‘X’: Enqueue element ‘X’ into the end of the nth queue. Returns true if the element is enqueued, otherwise false.

2: Dequeue the element at the front of the nth queue. Returns -1 if the queue is empty, otherwise, returns the dequeued element.
Enqueue means adding an element to the end of the queue, while Dequeue means removing the element from the front of the queue.
Input Format:
The first line of input contains two space-separated integers ‘N’ and ‘Q’ denoting the size of queue and number of queries, respectively. 

The next ‘Q’ lines specify the type of operation/query to be performed on the data structure.

Each query contains an integer ‘P’ denoting the type of query.

For query of type 1, the integer ‘P’ is equal to 1 and it is followed by one integer ‘X’ denoting the element on which operation is to be performed.

For query of type 2, the integer ‘P’ is equal to 2 which dequeues the element.
Output Format:
For each query, return the output returned after performing the corresponding operation on the data structure. 

Print the output of each test case in a separate line.
You don’t need to print anything. It has already been taken care of. You just have to complete the given functions.
1 <= N <= 1000
1 <= Q <= 10^5 
1 <= P <= 2
1 <= X <= 10^5

Time limit: 1 sec
Approach 1

In this approach, we will be implementing a circular queue using arrays. A circular queue has two key methods or purpose:


  1. enqueue():
    • Check whether the queue is full.
      • A queue is full when the front is next to the rear. For example, with a queue of size 6, if front is 0 and rear is 5, or if front is 2 and rear is 1, it means that the queue is full.
      • If it is full, then return false.
      • If the queue is not full, then check if rear is the last index.
        • If it is, set rear to 0;
        • If it is not, increment rear and add the value at that index.
  2. dequeue():
    • Check whether the queue is empty (i.e., if front/rear has a value of -1).
      • If it is empty, the return -1.
      • If the queue is not empty, then check if the queue has only one value (i.e., front == rear).
        • If it does have only one value, set both rear and front to -1.
        • If it does not, check if front is the last index of the queue and, if so, set front to 0, otherwise, increment front.
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