drawer-riddle.js

function shuffleArray(array) {
  for (let i = array.length - 1; i > 0; i--) {
      const j = Math.floor(Math.random() * (i + 1));
      [array[i], array[j]] = [array[j], array[i]];
  }
}

function alg(n) {
  const array = [...Array(n).keys()];
  shuffleArray(array);
  // console.log(`array: ${array}`);
  for (let i = 0; i < n; i += 1) {
    let temp = array[i];
    let attempt = 0;
    let target = i;
    while (attempt !== n / 2 && target < n) {
      // console.log(`i: ${i}, attempt: ${attempt}, temp: ${temp}, target: ${target}`)
      while (temp !== target && attempt !== n / 2) {
        const newTemp = array[temp];
        array[temp] = temp;
        temp = newTemp;
        // console.log(`after switch, temp: ${temp}, array[temp]: ${array[temp]}, array: ${array}`);
        attempt += 1;
      }

      target += 1;
    }

    if (array[i] !== i) {
      return false;
    }
  }

  return true;
}

function prob(n = 100, attempts = 100000) {
  const successes = [...Array(attempts).keys()].map(() => alg(n)).reduce((total, res) => {
    total += res ? 1 : 0;
    return total;
  }, 0);
  console.log(successes / attempts);
}

prob();