Stacks

First in, last out (FIFO)

• Create a Stack class with a constructor method which initializes an empty array.
• Define a push method which adds an element to the top of the stack. Can use unshift to add to the beginning of an array.
• Define a pop method which removes an element from the top of the stack. Can use shift to remove from the beginning of an array.
• Define a peek method which returns the element at the top of the stack, without removing it. Can refer to the first element in an array with [0] since arrays are zero-indexed.
• Define a isEmpty method which checks if the stack is empty. Uses the length property of an array to check if the array is empty.

Example:

const s = new Stack()
s.push(1)
s.push(2)
s.pop() // returns 2
s.pop() // returns 1

Making a Stack

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

  push(item) {
    this.items.unshift(item)
  }

  pop(item) {
    return this.items.shift()
  }

  peek(item) {
    return this.items[0]
  }

  isEmpty() {
    return this.items.length === 0
  }
}

Queue

First one in, first one out (FIFO)

Enqueue: add to the end of the queue. Dequeue: remove from the front of the queue.

A common way to make a queue is to make a queue class, which has initialized an empty array. This array has tons of built in methods, but we will only expose the unshift() and pop() methods, limiting it to a queue.

Description: Create a queue data structure. The queue should be a class with methods 'add' and 'remove'. Adding to the queue should store an element until it is removed.

Examples:

const q = new Queue()
q.enqueue(1)
q.dequeue() // returns 1;

q.isEmpty() // returns true;

q.enqueue('A')
q.enqueue('B')
q.enqueue('C')

q.peek() // returns 'A';

Making a Queue

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

  enqueue(item) {
    this.items.push(item)
  }

  dequeue(item) {
    return this.items.shift()
  }

  peek(item) {
    return this.items[0]
  }

  isEmpty() {
    return this.items.length === 0
  }
}