Chunky Monkey Challenge: Recursion Solution

JavaScript
1

Hi everyone, I just finished the JS Chunky Monkey Challenge, I solved it using a for loop and when I checked the challenge guide I saw that you could do it using recursion. I’ve been trying to wrap my head around it but I still don’t understand how, has anyone has an explanation for this? Thank you

That’s the code written on the guide (the goal is to write a function that splits an array (first argument) into groups the length of size (second argument) and returns them as a two-dimensional array.)

function chunkArrayInGroups(arr, size) {
  if (arr.length <= size) {
    return [arr];
  } else {
    return [arr.slice(0, size)].concat(
      chunkArrayInGroups(arr.slice(size), size)
    );
  }
}
2

This is actually very similar to the freeCodeCamp lesson on writing a recursive “countdown” function. The fact that everything is being done in that return statement probably makes it much harder to see. Does it help if I do this:

function chunkArrayInGroups(arr, size) {
  if (arr.length <= size) {
    return [arr];
  } else {
    const afterChunk = arr.slice(size);
    const oneChunk = arr.slice(0, size);
    const chunkedArr = chunkArrayInGroups(afterChunk, size);
    return [oneChunk].concat(
      chunkedArr
    );
  }
}
3 Likes
3

It does a little bit, thanks now I understand almost everything but I still have a problem understanding the afterChunk, we are using it as a argument with slice, means just a copy of the original array, as I see it, it’s always gonna be the first size elements? we are not changing where to start each time? If it makes sense.

4

afterChunk would be the part of the array from index size to the end of the array.

1 Like
5

Still have some issues with it so far :sweat_smile: but thank you so much for your help. I’ll keep searching about it

6

Feel free to ask more questions. It’s what we’re here for :smiley:

1 Like
7

I don’t know if it’s too late to jump in, but I was (and maybe still am a little) struggling to understand what’s going on. So I broke it down. I’m going to pass an array directly into the function for the arr argument, and 2 for the size argument, and then I’m going to go through each return statement for chunkArrayInGroups function:

// 1st function call:
chunkArrayInGroups(  [3, 4, 2, 8, 9, 10, 200 ],  2 ) );
    // its return statement: 
    // [ [3, 4] ].concat(chunkArrayInGroups( [2, 8, 9, 10, 200], 2 ) );

// 2nd function call:
chunkArrayInGroups( [2, 8, 9, 10, 200], 2 );
    // its return statement:
    // [ [2, 8] ].concat( chunkArrayInGroups( [9, 10, 200],  2 ) );

//  3rd function call: 
chunkArrayInGroups( [9, 10, 200],  2 );
    // its return statement: 
    // [ [9, 10] ].concat( chunkArrayInGroups( [200], 2 ) );

// 4th function call: 
chunkArrayInGroups( [200], 2 );
    // since it meets the if statment's condition ( [200].length <= 2 ),
    // it returns [ [200] ] 
    // which triggers the  whole returning process: 

[ [200] ] is returned which begins concatenation starting with to the 4th call of the chunkArrayInGroups function, 
//which returns [ [200] ] in the 4th function call and concatenates that to [ [9, 10] ] 
// which returns [ [9, 10], [200] ] in 3rd function call and concatenates that to [ [2, 8] ]
// which returns [ [2, 8], [9, 10], [200] ] in the 2nd function call and concatenates that to [ [3, 4] ]  
// which returns [ [3, 4] , [2, 8], [9, 10], [200] ] in the 1st function call, finishing the recursive function.```

Writing that out helped me to see what's happening better. I hope it helps you. I hope you have a great day.
2 Likes
8

Hey, thank you. This helps a lot and now and now I know what confused me, it’s because of the slice method, I find;t pay much attention to it so that’s what I thought was going on then:

// 1st function call:
chunkArrayInGroups(  [3, 4, 2, 8, 9, 10, 200 ],  2 ) );

// 2nd function call:
chunkArrayInGroups( [3, 4, 2, 8, 9, 10, 200 ], 2 );

//  3rd function call: 
chunkArrayInGroups([3, 4, 2, 8, 9, 10, 200 ],  2 );

As you can see it only makes scene the first time the function runs.

Thank you again for the explanation

9

You’re welcome. I’ve been doing my best to teach myself code by doing free tutorials and etc. I’m glad I could help even though I’m not a pro. Hopefully I will be able to get hired doing some remote work soon. Happy Coding!

1 Like
10

Best of luck man, hope you find a position soon

11

Thank you. :slight_smile:

1 Like