freeCodeCamp/guide/english/certifications/coding-interview-prep/data-structures/create-a-circular-queue/index.md

title
Create a Circular Queue

Create a Circular Queue

Method:

• In this challenge we create a Circular Queue data structure.
• First, we need to create an array of size with all elements set to null.
• Then we create an equeue method, which moves the write pointer but doesnt exceed the read pointer.
• The dequeue method on the other hand, moves the read pointer but doesnt exceed the write pointer.
• Example:
  • First, we create an array of length 5:

  [null, null, null, null, null]
   ^Read @ 0
   ^Write @ 0
  

  • Then we enqueue a, b, and c:

  [a, b, c, null, null]
   ^Read @ 0
            ^Write @ 3
  

  • Now we dequeue all the enqueued items:

  [null, null, null, null, null]
                     ^Read @ 3
                     ^Write @ 3
  

  • Finally, we enqueue d, e and f:

  [f, null, null, d, e]
                  ^Read @ 3
      ^Write @ 1
  

Solution:

class CircularQueue {
    constructor(size) {
 
      this.queue = [];
      this.read = 0;
      this.write = 0;
      this.max = size - 1;
 
      while (size > 0) {
         this.queue.push(null);
         size--;
      }
 
    }
 
    print() {
      return this.queue;
    }
 
 
    enqueue(item) {
     if (this.queue[this.write] === null){
       this.queue[this.write++] = item;
 
       if (this.write > this.max) this.write = 0;
       return item;
     }
     return null;
    }
 
    dequeue() {
      if (this.queue[this.read] != null){
        let item = this.queue[this.read];
        this.queue[this.read++] = null;
        if (this.read > this.max) this.read = 0;
        return item;
      }
      return null;
    }
 }

References:

• Wikipedia