Rotate the elements of an array to the left

Question

I am trying to solve a JavaScript challenge from jshero.net. The challenge is this:

Write a function rotate that rotates the elements of an array. All elements should be moved one position to the left. The 0th element should be placed at the end of the array. The rotated array should be returned. rotate(['a', 'b', 'c']) should return ['b', 'c', 'a'].

All I could come up with was this:

function rotate(a){
  let myPush = a.push();
  let myShift = a.shift(myPush);
  let myFinalS = [myPush, myShift]
  return myFinalS
}

But the error message I got was:

rotate(['a', 'b', 'c']) does not return [ 'b', 'c', 'a' ], but [ 3, 'a' ]. Test-Error! Correct the error and re-run the tests!

I feel like I'm missing something really simple but I can't figure out what. Are there other ways to solve this?

Zohaib Sohail · Accepted Answer · 2020-06-15 16:24:56Z

3

function rotate(array){
   let firstElement = array.shift();
   array.push(firstElement);
   return array;
}

answered Jun 15, 2020 at 16:24

Zohaib Sohail

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ROOT · Accepted Answer · 2020-06-15 16:26:29Z

2

To achieve the output you are looking for, first you have to use Array.shift() to remove the first element, then using Array.push() add the element back to the end of the Array, then return the array, the issue is that you used the wrong oder for these steps, also .push() method takes element to be added as argument, here is a working snippet:

function rotate(a){
  let myShift = a.shift();
  a.push(myShift);
  return a;
}

console.log(rotate(['a', 'b', 'c']));

answered Jun 15, 2020 at 16:26

ROOT

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1 Comment

DefNotBruceWayne Over a year ago

It's working now. Thank you for the explanation as well.

Nithish · Accepted Answer · 2020-06-15 16:31:13Z

1

Here I have created a utility where, the input array will not get mutated even after rotating the array as per the requirement.

function rotate(a){
  let inputCopy = [...a]
  let myShift = inputCopy.shift();
  let myFinalS = [...inputCopy, myShift]
  return myFinalS
}

console.log(rotate([1,2,3]))
console.log(rotate(["a","b","c"]))

Hope this helps.

answered Jun 15, 2020 at 16:31

Nithish

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Comments

index · Accepted Answer · 2020-11-24 17:39:00Z

arr.unshift(...arr.splice(arr.indexOf(k)))

Using unshift(), splice() and indexOf(), this is a one line that should help. arr is the array you want to rotate and k the item you want as first element of the array. An example of function could be:

let rotate = function(k, arr) {
    arr.unshift(...arr.splice(arr.indexOf(k)))
}

And this are examples of usage:

let array = ['a', 'b', 'c', 'd']
let item = 'c'

rotate(item, array)
console.log(array)

// > Array ["c", "d", "a", "b"]

Finally back to the original array:

rotate('a', array)
console.log(array)

// > Array ["a", "b", "c", "d"]

Peter Mortensen · Accepted Answer · 2023-08-22 21:12:48Z

0

Use:

function rotate(arr){
    let toBeLast = arr[0];
    arr.splice(0, 1);
    arr.push(toBeLast);
    return arr;
}
console.log(rotate(['a', 'b', 'c']));

edited Aug 22, 2023 at 21:12

Peter Mortensen

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answered Jun 15, 2020 at 16:50

tusharkashyap63

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