Coinflip calculator

coinflip_odds.js

const HEADS = 'heads';
const TAILS = 'tails';
const DESIRED_STREAK_COUNT = 10;
const DESIRED_RESULT = HEADS;

function start() {
  let attempts = 1;
  let totalFlips = 0;
  let streakCount = 0;
  let done = false;


  while (!done) {
    const result = coinFlip();
    totalFlips++;

    if (result === DESIRED_RESULT) {
      // Yay, desired result.
      streakCount++;
    } else {
      // Start all over.
      streakCount = 0;
      attempts++;
    }

    if (streakCount === DESIRED_STREAK_COUNT) {
      // We are done
      done = true;
    }
  }

  return { attempts, totalFlips };
}

function coinFlip() {
  return Math.round(Math.random()) === 0 ? HEADS : TAILS;
}

const TOTAL_RUNS = 500000;
let globalAttempts = 0;
let globalTotalFlips = 0;

for (let i = 0; i < TOTAL_RUNS; i++) {
  const { attempts, totalFlips } = start();
  globalAttempts += attempts;
  globalTotalFlips += totalFlips;
}
console.log(`${TOTAL_RUNS}`);
console.log(`On average ${globalAttempts / TOTAL_RUNS} attempts per run.`);
console.log(`On average ${globalTotalFlips / TOTAL_RUNS} flips per run.`);

// Some results:

// 2500
// On average 1034.838 attempts per run.
// On average 2066.8296 flips per run.

// 5000
// On average 1002.8526 attempts per run.
// On average 2003.4454 flips per run.

// 10000
// On average 1028.1834 attempts per run.
// On average 2054.4075 flips per run.

// 20000
// On average 1029.70735 attempts per run.
// On average 2057.75995 flips per run.

// 50000
// On average 1024.1241 attempts per run.
// On average 2046.05932 flips per run.

// 100000
// On average 1024.08843 attempts per run.
// On average 2046.14881 flips per run.

// 200000
// On average 1021.128585 attempts per run.
// On average 2040.19978 flips per run.

// 200000
// On average 1025.70776 attempts per run.
// On average 2049.322875 flips per run.

// 200000
// On average 1026.474355 attempts per run.
// On average 2050.808345 flips per run.

// 500000
// On average 1023.405016 attempts per run.
// On average 2044.827366 flips per run.