Little Puzzlers - Fun With Random numbers

random.js

describe('randomness', () => {

  function rand5() {
    let low = 1;
    let high = 5;
    return Math.floor(Math.random() * (high - low + 1) + low);
  }

  function createGenerator(min, max, func) {
    return { next: func, min, max };
  }

  function widen(generator) {
    return createGenerator(1, generator.max * generator.max, () => {
      let x = generator.next();
      let y = generator.next();
      return (x - 1) * generator.max + y;
    })
  }

  function narrow(generator, max) {
    return createGenerator(1, max, () => {
      do {
        let v = generator.next();
        if (v <= max)
          return v;
      } while(true);
    })
  }

  function changeMax(generator, max) {
    while (generator.max < max)
      generator = widen(generator);
    if (generator.max > max)
      generator = narrow(generator, max);
    return generator;
  }

  function showDistribution(generator) {
    let results = [];
    for (var i = 0; i < 100000; ++i) {
      let v = generator.next() - 1;
      results[v] = results[v] || 0;
      results[v]++;
    }
    console.log(results, results.map((v) => v / 100000))
  }

  it('show distributions', () => {
    let Rand5 = createGenerator(1, 5, rand5);
    showDistribution(Rand5);
    showDistribution(changeMax(Rand5, 4));
    showDistribution(changeMax(Rand5, 7));
    showDistribution(changeMax(Rand5, 30));
  })

})