Changing an array into a list using javascript

Question

Changing an array into a list using javascript

function convertArrayToList(inputArray) {
  let list = null;

  for (let i = inputArray.length - 1; i >= 0; i--) {
    list = { value: inputArray[i], rest: list };
  }

  return list;
}
let result = convertArrayToList([10, 20]);
console.log(JSON.stringify(result));

The output I am currently getting is:

{"value":10,"rest":{"value":20,"rest":{"rest":null}}}

But what I actually want is:

{value: 10, rest: {value: 20, rest: null}}

How can I solve this issue? Specifically, how do I change the last "rest" to null instead of another object?

javascript arrays list object

Answer 1

Answer №1

If you want to correct your code, make sure to assign i = arr.length - 1 as the initial value of i. Remember that arrays are 0-indexed, so the index of the last item is always one less than the length of the array:

function convertArrayToList(arr) {
  let rest = null

  for (let i = arr.length - 1; i >= 0; i--) {
    rest = { value: arr[i], rest };
  }

  return rest;
}

const result = convertArrayToList([10, 20]);
console.log(JSON.stringify(result));

An alternative approach would be using Array.reduceRight() to traverse the list from the end, setting the initial value as null:

const convertArrayToList = arr =>
  arr.reduceRight((rest, value) => ({
    value,
    rest
  }), null)

const result = convertArrayToList([10, 20]);
console.log(JSON.stringify(result));

Answer 2

If you want to correct your code, make sure to assign i = arr.length - 1 as the initial value of i. Remember that arrays are 0-indexed, so the index of the last item is always one less than the length of the array:

function convertArrayToList(arr) {
  let rest = null

  for (let i = arr.length - 1; i >= 0; i--) {
    rest = { value: arr[i], rest };
  }

  return rest;
}

const result = convertArrayToList([10, 20]);
console.log(JSON.stringify(result));

An alternative approach would be using Array.reduceRight() to traverse the list from the end, setting the initial value as null:

const convertArrayToList = arr =>
  arr.reduceRight((rest, value) => ({
    value,
    rest
  }), null)

const result = convertArrayToList([10, 20]);
console.log(JSON.stringify(result));

Answer 3

Answer №2

When dealing with array indexes, it's important to remember that they are 0 based. For example, in the array [10, 20], the index of 10 is 0 and the index of 20 is 1. If you start your loop from arr.length, which is 2 in this case, the first arr[i] will result in undefined, causing the loop to run one extra iteration. To avoid this issue when iterating backwards through an array, always begin at length - 1.

function array_to_list(arr) {
  list = null

  for (i = arr.length - 1; i >= 0; i--) {
    list = { value: arr[i], rest: list };
  }

  return list;
}
x = array_to_list([10, 20]);
console.log(JSON.stringify(x));

Answer 4

When dealing with array indexes, it's important to remember that they are 0 based. For example, in the array [10, 20], the index of 10 is 0 and the index of 20 is 1. If you start your loop from arr.length, which is 2 in this case, the first arr[i] will result in undefined, causing the loop to run one extra iteration. To avoid this issue when iterating backwards through an array, always begin at length - 1.

function array_to_list(arr) {
  list = null

  for (i = arr.length - 1; i >= 0; i--) {
    list = { value: arr[i], rest: list };
  }

  return list;
}
x = array_to_list([10, 20]);
console.log(JSON.stringify(x));

Changing an array into a list using javascript

Answer №1

Answer №2

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