How to use two Queues In Javascript

Using one Queue

In this approach, we are using two queues to implement the stack. we have created a class named stack and defined methods like push, pop, peek, clear and isEmpty. every methods has some conditions according to the need.

Example: This example shows the implementation of the above-explained approach.

JavaScript

 class Stack  {
      constructor() {
        this.queue1 = [];
        this.queue2 = [];
      }

      push(value) {
        // Push new element to queue1
        this.queue1.push(value);
      }
      
      pop() {
        if (this.isEmpty()) {
          return null; // Stack is empty
        }

        // Move all elements from queue1 to
        // queue2 except the last one
        while (this.queue1.length > 1) {
          this.queue2.push(this.queue1.shift());
        }

        // Pop the last element from queue1
        // (which is the top of stack)
        const popped = this.queue1.shift();

        // Swap queue1 and queue2
        [this.queue1, this.queue2] = [this.queue2, this.queue1];

        return popped;
      }

      peek() {
        if (this.isEmpty()) {
          return null;
        }
        return this.queue1[this.queue1.length - 1];
      }

      isEmpty() {
        return this.queue1.length === 0;
      }

      clear(){
          let tempQueue = this.queue1; 
          this.queue1 = [];
          this.queue2 = []; 
          return tempQueue;
      }
    }

   // Example usage:
    const stack = new Stack();
    stack.push(1)
    stack.push(2)
    stack.push(3)
    stack.pop()    
    stack.peek()
    console.log(stack.pop());  
    console.log(stack.peek());

Time complexity: O(n) for popping elements but other operation like ‘push’ have only 0(1) time complexity.

Space complexity: O(n) for storing elements in the queue.

JavaScript program to implement stack using queue

In this article, we implement a JavaScript program to make a stack using a queue data structure. It provides essential stack methods like push(), pop(), and peek(), isEmpty() operations, utilizing either one or two queues to simulate the behavior of a stack.

Examples:

Input:
push(2)
push(3)
pop()
peek()
push(4)
isEmpty()

Output:
 3 2  false

Explanation:
push(2): The stack will be {2}
push(3): The stack will be {2 3}
pop():Pops last element (3), stack will be {2}
peek(): Peek top element of the stack 2
push(4): The stack will be {2 4}
isEmpty(): The stack is not empty so its "false".


Input:
push(1)
push(2)
push(3)
pop()
peek()
clear()

Output: 3 2 

Explanation:
push(1): The stack will be {1}
push(2): The stack will be {1,2}
push(3): The stack will be {1,2,3}
pop(): It pops last element (3), stack will be {1,2}
peek(): It peeks top element of the stack 2
clear() stack will be {}

These are the following approaches:

Table of Content

Using one Queue
Using two Queues

Tags:

#JavaScript-DSA #JavaScript #Web Technologies

Using one Queue

How to use two Queues In Javascript

JavaScript program to implement stack using queue

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