Array Left Rotation in Javascript will log to console but not return

Question

I'm working on the array left rotation on Hackerrank. The solution that I have will console.log the array containing the correct result, but will not work using return. Here's the detail from their site - "Print a single line of n space-separated integers denoting the final state of the array after performing d left rotations." I've read that the issue might be with asynchronous functions running in node.js, but I'm not sure how to work around that.

// sample input - 1 2 3 4 5
// sample output - 5 1 2 3 4

function rotLeft(a, d) {
  var arr = [];

    for (var i = 1; i <= a; i++){
      arr.push(i)
    };
    for (var j = 1; j <= d; j++){
    	arr.shift(arr.push(j))
    }
    console.log(arr.toString()); // <-- this will print the desired output.
    return arr.toString(); // <-- no return from this.
}


rotLeft(5, 4)

Answer 1

I have also been trying to solve this problem. There are some issues in your current solution. See you have to create an array and store the array passed from parameters in it. What you have done is just creating a new array and adding the sequence of numbers of elements that should be in it e.g a.length=5 you are doing arr.push 1 2 3 4 5. But the question wants an array of user's choice. Second thing is that you should return an array not the string.

So this is the solution of this problem:

function rotLeft(a, d) {
    var arr = [];
    for (var i = 0; i < a.length; i++) {
        arr.push(a[i]);
    };
    for (var j = 1; j <= d; j++) {
        arr.shift(arr.push(arr[0]));
    }
    return arr;
}

Answer 2

I'll give my solution to this problem for future visitors.

you can do this in one line as follows :

function rotLeft(a, d)
 {
    let rslt = a.slice(d).concat(a.slice(0,d));
    return rslt
 }

You need to split the initial array at the d'th position in two parts, and simply swap those two.

The slice() method returns a shallow copy of a portion of an array into a new array object selected from begin to end (end not included). The original array will not be modified.

var animals = ['ant', 'bison', 'camel', 'duck', 'elephant'];

console.log(animals.slice(2));
// expected output: Array ["camel", "duck", "elephant"]

console.log(animals.slice(2, 4));
// expected output: Array ["camel", "duck"]

console.log(animals.slice(1, 5));
// expected output: Array ["bison", "camel", "duck", "elephant"]