Rotate an Array K Times in Python

The challenge

Given an array, rotate the array to the right by k steps, where k is non-negative.

Example 1:

Input: nums = [1,2,3,4,5,6,7], k = 3
Output: [5,6,7,1,2,3,4]
Explanation:
rotate 1 steps to the right: [7,1,2,3,4,5,6]
rotate 2 steps to the right: [6,7,1,2,3,4,5]
rotate 3 steps to the right: [5,6,7,1,2,3,4]

Example 2:

Input: nums = [-1,-100,3,99], k = 2
Output: [3,99,-1,-100]
Explanation: 
rotate 1 steps to the right: [99,-1,-100,3]
rotate 2 steps to the right: [3,99,-1,-100]

Constraints:

  • 1 <= nums.length <= 2 * 10^4
  • It’s guaranteed that nums[i] fits in a 32 bit-signed integer.
  • k >= 0

The solution in Python

Option 1 could be as follows:

# update an array/list in-place
def rotate(self, nums: List[int], k: int) -> None:
    # loop `k` amount of times
    for i in range(k):
        # set previous temp variable
        # .. to the last item
        prev = nums[-1]
        # loop through the array/list
        for j in range(len(nums)):
            # swap the elements
            nums[j], prev = prev, nums[j]

Another way to do this is to make use of Python’s Splicing methodology:

# update an array/list in-place
def rotate(self, nums: List[int], k: int) -> None:
    k %= len(nums)
    nums[k:], nums[:k] = nums[:-k], nums[-k:]
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