jellybeanSim.js

// A crude simulation of Wait but why's Jellybean Problem
// http://waitbutwhy.com/2016/03/the-jellybean-problem.html

// This is the simulation:
// Randomly pick a number between 1 and 3 (this is the wining choice)
// Randomly pick a second number between 1 and 3 (this is the player's first choice)
// Compare the two numbers:
//   - If they are the same, sticking to first choice will win, switchers will lose
//   - If they are different, sicking to the first choice will lose, switchers will win

function getRandomIntInclusive(min, max) {
  return Math.floor(Math.random() * (max - min + 1)) + min;
}

var numSimulations = 300000
var currentSimulation = 1
var switchers = 0
var nonswitchers = 0

while (currentSimulation < numSimulations + 1) {
  if (getRandomIntInclusive(1,3) == getRandomIntInclusive(1,3)) {
    // Non-switchers win!
    nonswitchers++
  } else {
    // Switchers win!
    switchers++
  }
  currentSimulation++
}

console.log("Out of " + numSimulations + " simulations...")
console.log("If you didn't switch you won " + nonswitchers + " times (" + (nonswitchers/numSimulations * 100).toPrecision(2) + "%)")
console.log("If you switched you won " + switchers + " times (" + (switchers/numSimulations * 100).toPrecision(2) + "%)")