collatz.js

// mreed4 committed on Aug 4, 2021

function randNum() {
  return Math.floor(Math.random() * 1000000);
}

function collatz(num = randNum()) {
  // num = parseInt(prompt(`Input any number`)); // User input
  const initialNumber = num; // Save number before it mutates

  // console.log({initialNumber});

  let arr = [num]; // Initialize array

  while (num != 1 && num > 0) {
    // Ensures no infinite loop

    if (num % 2 === 0) {
      num /= 2;
      arr.push(num);
    } else {
      num = num * 3 + 1;
      arr.push(num);
    }
  }

  // console.log(arr);

  // Returns new array of the last digits in each number in arr
  let arr2 = arr.map((int) => {
    int = int.toString();
    return parseInt(int[int.length - 1], 10);
  });

  // console.log(arr2);

  let binArr = arr2.reverse().map((int) => int % 2);

  let data = [];
  for (let i = 0; i < binArr.length; i += 4) {
    // let input = binArr.slice(i, i + 4).join("");
    // data.push(Number(parseInt(input, 2).toString(10)))
    data.push(binArr.slice(i, i + 4).length);
  }

  // console.log(data)
  // console.log(arr)
  let steps = arr.length;
  // console.log(`${initialNumber} took ${steps} steps to resolve to 1`)
  let max = Math.max(...arr);
  let maxStep = arr.indexOf(max);
  // max = max.toLocaleString();
  // console.log(`The largest number was ${max} at step ${maxStep}`)
  return [{ initialNumber }, { steps }, { max }, { maxStep }];
}

collatz();

let arr3 = [];

for (let i = 1; i <= Math.pow(10, 3); i++) {
  arr3.push(collatz(i));
}

console.log(arr3);

// let arr9232 = arr3.filter(item => item[2] === "9,232").sort(item => ite)

// console.log(arr9232)