montehall.js

/*!
 * Usage:
 * $ node montehall.js
 * $ DEBUG=1 node montehall.js
 *
 * changeYourMind=true
 *
 * $ node montehall.js | grep won | wc -l
 * ~660
 *
 * changeYourMind=false
 *
 * $ node montehall.js | grep won | wc -l
 * ~330
 */
const util = require('util');
const DEBUG = process.env.DEBUG;

function getRandomInt(max) {
  return 1 + Math.floor(Math.random() * max);
}

function getRandomValue(list) {
  return list[Math.floor(Math.random() * list.length)];
}

function debug(msg) {
  if (DEBUG) {
    console.log(util.styleText('grey', msg));
  };
}

/**
 * @param {bool} changeYourMind
 */
function playMonteHall(changeYourMind) {
  var doors = [ '#1', '#2' ,'#3' ];

  var secret = getRandomValue(doors);
  var choice = getRandomValue(doors);
  console.log('You choose door ' + choice);
  debug('... prize is behind ' + secret);

  var allGoats = doors.filter(value => value !== secret);
  debug('... all goats: ' + allGoats);

  var remainingGoats = allGoats.filter(value => value !== choice);
  debug('... remaining goats: ' + remainingGoats);

  var shownGoat = getRandomValue(remainingGoats);
  console.log('Goat behind door ' + shownGoat);

  var remainingDoor = doors.filter(value => value !== choice && value !== shownGoat)[0];
  console.log('Do you want to change to door ' + remainingDoor + '?');

  if (!changeYourMind) {
    console.log('[STICK]',
      secret === choice
        ? util.styleText('green', 'You won!')
        : util.styleText('red', `You lost, it was door ${secret}.`)
    );
  } else {
    var newChoice = remainingDoor;
    console.log('[CHANGE]',
      secret === newChoice
        ? util.styleText('green', 'You won!')
        : util.styleText('red', `You lost, it was door ${secret}.`)
    );
  }
}

var i = 1000;
while (i--) {
  playMonteHall(true);
}

/*

  # START

  3 starting layouts
  [ 🏆  ] [ 🐐  ] [ 🐐  ]
  [ 🐐  ] [ 🏆  ] [ 🐐  ]
  [ 🐐  ] [ 🐐  ] [ 🏆  ]

  3 starting choices
  [   🔹] [     ] [     ]
  [     ] [ 🔹  ] [     ]
  [     ] [     ] [   🔹]

  9 starting scenarios
  [ 🏆🔹] [ 🐐  ] [ 🐐  ]
  [ 🏆  ] [ 🐐🔹] [ 🐐  ]
  [ 🏆  ] [ 🐐  ] [ 🐐🔹]
  [ 🐐🔹] [ 🏆  ] [ 🐐  ]
  [ 🐐  ] [ 🏆🔹] [ 🐐  ]
  [ 🐐  ] [ 🏆  ] [ 🐐🔹]
  [ 🐐🔹] [ 🐐  ] [ 🏆  ]
  [ 🐐  ] [ 🐐🔹] [ 🏆  ]
  [ 🐐  ] [ 🐐  ] [ 🏆🔹]

  Chance of win:
    3 in 9
  = 1 in 3
  = 33%

  ---------

  # THE GOAT

  9 starting scenarios        show you the one or two remaining goats (not prize, not choice)
  [ 🏆🔹] [ 🐐  ] [ 🐐  ]
                              [ 🏆🔹] [ 🐐❌] [ 🐐2️⃣]
                              [ 🏆🔹] [ 🐐2️⃣] [ 🐐❌]
  [ 🏆  ] [ 🐐🔹] [ 🐐  ]
                              [ 🏆2️⃣] [ 🐐🔹] [ 🐐❌]
                              [ 🏆2️⃣] [ 🐐🔹] [ 🐐❌]
  [ 🏆  ] [ 🐐  ] [ 🐐🔹]
                              [ 🏆2️⃣] [ 🐐❌] [ 🐐🔹]
                              [ 🏆2️⃣] [ 🐐❌] [ 🐐🔹]
  [ 🐐🔹] [ 🏆  ] [ 🐐  ]
                              [ 🐐🔹] [ 🏆2️⃣] [ 🐐❌]
                              [ 🐐🔹] [ 🏆2️⃣] [ 🐐❌]
  [ 🐐  ] [ 🏆🔹] [ 🐐  ]
                              [ 🐐2️⃣] [ 🏆🔹] [ 🐐❌]
                              [ 🐐❌] [ 🏆🔹] [ 🐐2️⃣]
  [ 🐐  ] [ 🏆  ] [ 🐐🔹]
                              [ 🐐❌] [ 🏆2️⃣] [ 🐐🔹]
                              [ 🐐❌] [ 🏆2️⃣] [ 🐐🔹]
  [ 🐐🔹] [ 🐐  ] [ 🏆  ]
                              [ 🐐🔹] [ 🐐❌] [ 🏆2️⃣]
                              [ 🐐🔹] [ 🐐❌] [ 🏆2️⃣]
  [ 🐐  ] [ 🐐🔹] [ 🏆  ]
                              [ 🐐❌] [ 🐐🔹] [ 🏆2️⃣]
                              [ 🐐❌] [ 🐐🔹] [ 🏆2️⃣]
  [ 🐐  ] [ 🐐  ] [ 🏆🔹]
                              [ 🐐❌] [ 🐐2️⃣] [ 🏆🔹]
                              [ 🐐2️⃣] [ 🐐❌] [ 🏆🔹]


  18 choices:
  *  6 in 18: on the prize, change to goat
  * 12 in 18: on the goat, change to prize

*/