LeetCode #189

Rotate an array of n elements to the right by k steps.

For example, with n = 7 and k = 3, the array [1,2,3,4,5,6,7] is rotated to [5,6,7,1,2,3,4].

What the question really means

I have no idea what “rotate by k steps” means. But from LeetCode’s test cases it looks like this:

nums = [1, 2, 3, 4, 5], k = 3, expected: keep the last k items, and move the front items to the end.

Another challenge is I have to do in-place mutation to the original array. So I need to use mutating functions such as:

  • Array.prototype.splice
  • Array.prototype.reverse
  • Array.prototype.push
  • Array.prototype.shift
  • Array.prototype.pop
  • etc.

Pseudo code

  1. Get the real “k” by k % nums.length because rotating n or n’s multiple steps doesn’t change the array.
  2. Use Array.prototyp.splice to remove the front items, and save the removed items to a variable.
  3. Loop the removed items array and add every items back to the end of the remaining array.


See the Pen 89. Rotate Array by Cherry Wang (@chryw) on CodePen.