TT Interview Solutions

Queues-using-stacks.md

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

  peek() {
    return this.arr[this.arr.length - 1]
  }

  push(n) {
    this.arr.push(n);
  }

  pop() {
    if (this.arr.length) {
      return this.arr.pop();
    }
    return null;
  }

  print() {
    console.log(this.arr);
  }
}

class Queue {
  constructor() {
    this.main = new Stack();
    this.aux = new Stack();
  }

  peek() {
    while (this.main.peek()) {
      this.aux.push(this.main.pop());
    }

    const e = this.aux.peek();

    while (this.aux.peek()) {
      this.main.push(this.aux.pop());
    }

    return e;
  }

  push(n) {
    this.main.push(n);
  }

  dequeue() {
    while (this.main.peek()) {
      this.aux.push(this.main.pop());
    }

    const e = this.aux.pop();

    while (this.aux.peek()) {
      this.main.push(this.aux.pop());
    }

    return e;
  }
}