JavaScript Recursion: Get the length of an array using recursion without accessing its length property

Question

Get the length of an array using recursion without accessing its length property.

My Code Below:

function getLength(array, count=0) {

  if (array.length === 0){
    return 0
  }

  else {
    count ++; 

    array.pop()
    return getLength(array, count)
  }
  return count; 
}

// To check if you've completed the challenge, uncomment these console.logs!
console.log(getLength([1])); // -> 1
console.log(getLength([1, 2])); // -> 2
console.log(getLength([1, 2, 3, 4, 5])); // -> 5
console.log(getLength([], 0)); // -> 0

When I run my code on the third console.log:

console.log(getLength([1, 2]));

it returns 0 instead of 2

What am I doing wrong?

///////////////////////////////////////////////////////////////////////////

figured it out:

function getLength(array, count=0) {

  if (array.length === 0){
    return count
  }

  else {
    count ++; 

    array.pop()
    return getLength(array, count)
  } 
}

@ninaScholz no, I'm not sure wether the OP uses us to solve code challenges. Thats up to a debate. — Jonas Wilms
– Jonas Wilms, Commented Jun 14, 2019 at 21:14

Nina Scholz · Accepted Answer · 2019-06-14 21:22:07Z

2

You could check if the item at index zero exists. This works only for non sparse arrays.

function getLength(array) {
    return 0 in array ? 1 + getLength(array.slice(1)) : 0;
}

console.log(getLength([1]));             // 1
console.log(getLength([1, 2]));          // 2
console.log(getLength([1, 2, 3, 4, 5])); // 5
console.log(getLength([], 0));           // 0

answered Jun 14, 2019 at 21:22

Nina Scholz

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Comments

Scott Sauyet · Accepted Answer · 2019-06-15 00:26:28Z

1

Another simple solution (which also does not work on sparse arrays) is

const len1 = arr => arr.reduce(n => n + 1, 0)

And a related, but less simple, one does work on sparse arrays:

const len2 = (arr) => Array.from(arr, _ => 1).reduce(n => n + 1, 0)

answered Jun 15, 2019 at 0:26

Scott Sauyet

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