Monty Hall problem: Simulation

monty-hall.js

#!/usr/bin/env node
'use strict';

function makeADeal (changeDoor, initialDoorNumber) {
  if (initialDoorNumber && (initialDoorNumber < 1 || initialDoorNumber > 3))
    throw new Error('If provided, the inital door number must be 1, 2, or 3.');
  function randomInt (max = 1, min = 0) {
    return Math.floor(Math.random() * (max - min + 1)) + min;
  }

  const lose = 'goat';
  const win = 'car';

  const doors = new Array(3).fill(lose);
  doors[randomInt(doors.length - 1)] = win;

  const selection = initialDoorNumber
    ? initialDoorNumber - 1
    : randomInt(doors.length - 1);
  if (!changeDoor)
    return {
      doors,
      result: doors[selection],
      win: doors[selection] === win,
    };

  const remaining = [...doors];
  remaining.splice(selection, 1);

  for (const [index, door] of remaining.entries()) {
    if (door === lose) {
      remaining.splice(index, 1);
      break;
    }
  }

  const result = remaining.pop();
  return {doors, result, win: result === win};
}

function simulate (iterations, changeDoor, initialDoorNumber) {
  let wins = 0;
  let losses = 0;
  for (let i = 0; i < iterations; i++) {
    makeADeal(changeDoor, initialDoorNumber).win ? wins++ : losses++;
  }
  return {
    iterations,
    losses,
    wins,
    win_percentage: 100 * (wins / iterations),
    changed: changeDoor ? true : false,
  };
}

const one = makeADeal(true, 2);
const many = simulate(1000, true);
console.log({one, many});