Intermediate Algorithm Scripting - Steamroller

JavaScript
1

Tell us what’s happening:
Describe your issue in detail here.

I tried it simply with a single reduce function to see what it gave back and it flattened everything but the deepest array. Then I attempted to add an index to the reduce function and also add a conditional statement that should have caught if the index was an array, to concatenate current[index] to the acc variable…but it tells me now that “acc” is undefined, and I am unsure why that is when the variable was declared at the beginning of the reduce function…

Your code so far

function steamrollArray(arr) {

  let flattened = arr.reduce((acc, current, index) => {
    if (Array.isArray(current)) {
      acc.concat(current[index]);
    } else {
      acc.concat(current);
    }
  }, []);

  return flattened;
}

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

Your browser information:

User Agent is: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:109.0) Gecko/20100101 Firefox/112.0

Challenge: Intermediate Algorithm Scripting - Steamroller

Link to the challenge:

2

A single loop isn’t going to cut it here. This is a tricky problem. You need to keep flattening until all the nested arrays are flattened out.

Your callback to reduce needs to return the updated value of acc or the result is automatically undefined.

3

ohh…okay…so recursion is absolutely necessary here it seems. I’ll try to make it recursive using the reduce function as the recursive return and add a base case.

4

Recursion or some sort of while loop. Recursion is the way I approached it.

5

yeah, I’ll try it…most times I shy away from recursion because I always managed to break the call stack lol…but hm, didn’t think of a while loop…even though those break the call stack as much as recursion does. But it’s an idea to try before a recursive call. I’ll have to think for a while to make a semi-successful recursive call. Might try that while loop first. :slight_smile:

1 Like
6

This was the recursion I came up with, but something’s wrong with it cause it broke the call stack…lol

function steamrollArray(arr) {

  let copy = [...arr];

  let flattened = [];
  
  // base case
  if (copy.length === 0) {
    return flattened;
  }

  // recursion
  if (Array.isArray(copy[0])) {
    flattened.push(copy[0].reduce((acc, current) => acc.concat(current)), []);
  } else {
    flattened.push(copy[0]);
  }

  return steamrollArray(flattened, arr, arr.slice(1));
}

console.log(steamrollArray([1, [2], [3, [[4]]]]));
8

I could try that. Thanks for the tip. :heart:

9

You still need some sort of recursion or while loop to handle the arbitrary depth nesting.

10

So the call I have in the new code “steamrollArr(…)” is not functioning as a recursive call??

11

The recursion here is tricky. You need a nested loop of some sort.

This would work fine if current was a flat array itself. But it isn’t always flat. How could you flatten it?

12

Oh, no, I meant with the new code I put up a couple of posts ago…this is the recursive code I added after the initial code, but this code is breaking the call stack:

function steamrollArray(arr) {

  let copy = [...arr];

  let flattened = [];
  
  // base case
  if (copy.length === 0) {
    return flattened;
  }

// recursion
  if (Array.isArray(copy[0])) {
    flattened.push(copy[0].reduce((acc, current) => acc.concat(current)), []);
  } else {
    flattened.push(copy[0]);
  }

  return steamrollArray(flattened, arr, arr.slice(1));
}

console.log(steamrollArray([1, [2], [3, [[4]]]]));
13

Right, I meant both of your codes. You need to combine the ideas in the two.

You need to loop over the array contents somehow.

Also, you can’t pass different arguments that are declared.

vs

14

okay, I’ll try to do that. With the passing in of declared arguments, did you mean the “arr” variable I passed in at the end? I thought you had to pass them into the recursion so that those variables aren’t lost on each loop…that’s why I added them a the end, was I not supposed to? Or, actually should I replace that with “copy” since I used that instead of “arr” for the manipulation.

15

Here you say that steamrollArray() only takes one argument. Any other arguments passed cannot be used because you only declared one parameter.

16

ohhhh…lol I get it…it’s not even looking for any parameters aside from that one passed in variable so it only has one it’s going to keep track of in the first place.

1 Like
17

You can get at other arguments via the arguments object, but really, you only need the arr to flatten as an argument.

1 Like
18

This topic was automatically closed 182 days after the last reply. New replies are no longer allowed.