monty-hall.js

proveWithStats(100000)

function proveWithStats(steps) {
    const winStats = {change: 0, keep: 0}

    for (let i = 0; i < steps/2; i++) {
        playRound('keep', winStats)
        playRound('change', winStats)
    }
    
    return winStats
}

function playRound(strategy, stats) {
    const doors = setUpDoors()
    let choice = rnd(3)
    const openDoor = openOneDoor(doors, choice)
    
    if (strategy == 'change') choice = change(choice, openDoor)
    
    const result = doors[choice]
    
    stats[strategy] += result
}

function rnd(limit) {
    return Math.floor(Math.random() * limit)
}

function setUpDoors() {
    const doors = [0, 0, 0]

    doors[rnd(3)] = 1
    
    return doors    
}

function openOneDoor(doors, choice) {
    const availableDoors = []

    for (const i in doors) {
        if (i != choice && doors[i] == 0){
            availableDoors.push(i)
        }
    }
    return availableDoors[rnd(availableDoors.length)] 
}

function change(choice, openDoor) {
    for (let i = 0; i < 3; i++){
        if (i != choice && i != openDoor){
            return i
        }
    }
}