Suppose you're on a game show, and you're given the choice of three doors: Behind one door is a car; behind the others, goats. You pick a door, say No. 1, and the host, who knows what's behind the doors, opens another door, say No. 3, which has a goat. He then says to you, "Do you want to pick door No. 2?" Is it to your advantage to switch your …

monty_hall.js

// Inspired by the movie 21. I wanted to run a simulation to better understand the
// problem and test to see if the odds really do shift to 66%. 
// Spoiler Alert: They do! 
// NOTE: Also swapped llamas for goats since they are way cooler

// Generate a random number between 1 and 3
function getNum() {
  return Math.floor(Math.random() * 3) + 1
}

// Build array of selections
const doorWithCar = Array(1000)
  .fill('')
  .map(() => {
    return getNum()
  })

// Objects that hold the cound of right and wrong answers
const noSwitch = {
  right: 0,
  wrong: 0,
}

const doesSwitch = {
  right: 0,
  wrong: 0,
}

function openLlamaDoor(doorWithCar, chosen) {
  // cannot open the door with a car
  // cannot open the door that the person chose
  // need to "getNum" until door is not door with car or chosen door
  let openedDoor = null
  do {
    openedDoor = getNum()
  } while (openedDoor === doorWithCar || openedDoor === chosen)
  return openedDoor
}

function checkSwitch(selection, car, llama) {
  let vals = [1, 2, 3]
  // remove llama
  const llamaIndex = vals.indexOf(llama)
  vals.splice(llamaIndex, 1)
  const selectionIndex = vals.indexOf(selection)
  vals.splice(selectionIndex, 1)
  const switchSelection = vals[0]
  switchSelection === car ? (doesSwitch.right += 1) : (doesSwitch.wrong += 1)
}

function checkNoSwitch(selection, car) {
  selection === car ? (noSwitch.right += 1) : (noSwitch.wrong += 1)
}

doorWithCar.forEach(car => {
  // choose a door
  const thisChoice = getNum()
  const llamaDoor = openLlamaDoor(car, thisChoice)
  checkNoSwitch(thisChoice, car)
  checkSwitch(thisChoice, car, llamaDoor)
  console.log('Did Not Switch', noSwitch)
  console.log('Did switch', doesSwitch)
})