Flatten an Arrray

1 
function flatten(arr){
    let newArr = [];
    console.log(arr)
    if (arr.length === 0) {
        return newArr;
    } 
    if(Array.isArray(arr[0])){
        let conc = newArr.concat(flatten(arr[0]))
        return newArr.concat(conc)
    } else{
        newArr.push(arr[0])
    }
    newArr = newArr.concat(flatten(arr.splice(1)))
    return newArr;
}
  flatten([1, [2, [3, 4], [[5]]]]) // [1, 2, 3, 4, 5].

I am taking the Udemy Course of algorithms and data structures. The goal is to write a function that will flatten an array. For example if the argument passed in is

  flatten([1, [2, [3, 4], [[5]]]])

the function should return

[1, 2, 3, 4, 5]

My function does not seem to account for the deeply nested 5 on the last index of the array. I’m not sure why it doesn’t .

I have been keeping track of what the algorithm is trying to do by using the site below.
http://pythontutor.com/visualize.html#mode=edit

2

This seems to fall more in line as to what I wanted it to do. However, I still can’t pass the test.

function flatten(arr){
    let newArr = [];
    console.log(arr)
    if (arr.length === 0) {
        return newArr.concat(newArr);
    } 
    if(Array.isArray(arr[0])){
         flatten(arr[0])
    } else{
        newArr.push(arr[0])
    }
    newArr = newArr.concat(flatten(arr.splice(1)))
    return newArr;
}
  flatten([1, [2, [3, 4], [[5]]]]) // [1, 2, 3, 4, 5].
3

In this line you aren’t doing anything with value returned by flatten(arr[0]).

4

the reason it is skipping the 5 is because your only sending arr[0] back into the function so when it becomes this [ [ 3, 4 ], [ [ 5 ] ] ] its only sending [3, 4] back in and [ [ 5 ] ] is lost

1 Like
5

If it’s any help, freeCodeCamp has this same challenge. It’s called Steamroller. It might be helpful to work on the challenges that lead up to it.

6

Yes, so the next step was to find how to access one index after another. Here is what i came up with

function flatten(arr){
    let newArr = [];
    console.log(arr)
    if (arr.length === 0) {
        return newArr.concat(newArr);
    } 
    if(Array.isArray(arr[0])){
         newArr = newArr.concat(flatten(arr[0]))
    } else{
        newArr.push(arr[0])
    }
    newArr = newArr.concat(flatten(arr.splice(1)))
    return newArr;
}
  flatten([1, [2, [3, 4], [[5]]]]) // [1, 2, 3, 4, 5].
7

Congratulations on finding a solution! Happy coding.

1 Like
8

Thank you!. That one was tough.