JavaScript Exercises: Merge two stacks into one

JavaScript Stack: Exercise-20 with Solution

Write a JavaScript program to merge two stacks into one.

Sample Solution:

JavaScript Code:

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

  push(element) {
    this.items.push(element);
  }
  pop() {
    if (this.isEmpty()) {
      return "Underflow";
    }
    return this.items.pop();
  }
  peek() {
    return this.items[this.items.length - 1];
  }
  isEmpty() {
    return this.items.length === 0;
  }
  size() {
    return this.items.length;
  }
  
 merge(stack2) {
    let stack1 = this.items;
    while (stack2.length > 0) {
      stack1.push(stack2.pop());
    }
    return stack1;
  }
  
displayStack(stack) {
  console.log("Stack elements are:");
  let str = "";
  for (let i = 0; i < stack.items.length; i++)
    str += stack.items[i] + " ";
  return str.trim();
 }      
}
let stack1 = new Stack();
stack1.push(10);
stack1.push(20);
stack1.push(30);
console.log("Stack-1");
console.log(stack1.displayStack(stack1));
let stack2 = new Stack();
stack2.push(40);
stack2.push(50);
stack2.push(60);
stack2.push(70);
console.log("Stack-2");
console.log(stack2.displayStack(stack2)); 
let result_merged_stack = stack1.merge(stack2.items); 
console.log("Merged Stack:");
console.log(result_merged_stack);

Sample Output:

Stack-1
Stack elements are:
10 20 30
Stack-2
Stack elements are:
40 50 60 70
Merged Stack:
[10,20,30,70,60,50,40]

Flowchart:

Live Demo:

See the Pen javascript-stack-exercise-20 by w3resource (@w3resource) on CodePen.

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