Intermediate Algorithm Scripting Question: Steam Roller

JavaScript
1

Hello,

I spent a few hours trying to figure this one to no avail. After checking the first answer, the recursive solution makes a lot of senses to me but I am have a hard time getting around what is happening with the rest operator:

function steamrollArray(arr) {
  const flattenedArray = [];
  // Loop over array contents
  for (let i = 0; i < arr.length; i++) {
    if (Array.isArray(arr[i])) {
      // Recursively flatten entries that are arrays
      //  and push into the flattenedArray
      flattenedArray.push(...steamrollArray(arr[i]));
    } else {
      // Copy contents that are not arrays
      flattenedArray.push(arr[i]);
    }
  }
  return flattenedArray;
};

// test here
steamrollArray([1, [2], [3, [[4]]]]);

I added some tests:

function steamrollArray(arr) {
  const flattenedArray = [];
  for (let i = 0; i < arr.length; i++) {
    if (Array.isArray(arr[i])) {
      console.log(arr[i]);
      flattenedArray.push(...steamrollArray(arr[i]));
    } else {
      console.log('Add ' + arr[i]);
      flattenedArray.push(arr[i]);
    }
  }
  console.log('Result ' + flattenedArray);
  return flattenedArray;
}

steamrollArray([1, [2], [3, [[4]]]]);

I get the same result with or without the spread operator.
It won’t pass the freecodecamp test however.

Can someone explain to me what’s going on here?

2

Is there something you don’t understand about the solution?
Without the spread operator, flattenedArray just gets an array pushed onto it, not individual values.

1 Like
3

I have added spoiler tags to this code since you posted a solution.

Your console.log() is misleading. I would instead use

console.log(steamrollArray([1, [2], [3, [[4]]]]));
1 Like
4

I actually I just found out that console.log output was misleading because of how I setup my test. Ie:

A friend told me its got something to do with implicit type conversion.

function steamrollArray(arr) {
  const flattenedArray = [];
  for (let i = 0; i < arr.length; i++) {
    if (Array.isArray(arr[i])) {
      console.log(arr[i]);
      flattenedArray.push(steamrollArray(arr[i]));
    } else {
      console.log('Add ' + arr[i]);
      flattenedArray.push(arr[i]);
    }
  }
  console.log('Result ' + flattenedArray);
  return flattenedArray;
}

steamrollArray([1, [2], [3, [[4]]]]);

module.exports = steamrollArray;

This is what was causing the problem . The output was misleading. Now that the output is giving me what I am expecting there is no confusion. :wink:

5

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