Monty Hall Problem

monty_hall.js

// Amount of time to run the problem
const RUN_TIMES = 10000

const runProblem = (change) => {
  // Starts with 3 doors containing nothing
  const chances = ['nothing', 'nothing', 'nothing']
  // Puts money behind one of the three doors randomly
  chances[Math.floor(Math.random() * 3)] = 'money'

  // Picks one of the doors randomly
  const choice = Math.floor(Math.random() * 3);

  // If choice should not change, returns the result with what is behind that door
  if (!change) {
    return chances[choice]
  }

  // Removes the door chosen
  chances.splice(choice, 1)

  // If there is still money behind one of the doors
  // This is important, as the host always knows this, and will never open a door with money
  if (chances.indexOf('money') > -1) {
    // Remove the door without the money
    chances.splice(chances.indexOf('nothing'), 1)
    // Returns the result with what is behind the door left
    return chances[0]
  }

  // If there is no money behind one of the doors, remove any door randomly
  chances.splice(Math.floor(Math.random() * 2), 1)
  // Returns the result with what is behind the door left
  return chances[0]
}

const results = {
  money: 0,
  nothing: 0
}

for (let x = 0; x < RUN_TIMES; x++) {
  const choice = runProblem(true)
  // Increments the on the results whatever came back
  results[choice]++
}

// Prints results
console.log(results);