Problem

Solution

Intuition

This problem requires us to return an array of length 2*len(nums) where result[i] = result[i+len(nums)] = nums[i]. Python offers an easy approach with just returning nums+nums and this will concatanate the arrays for you; however, to explain to an interviewer, we break this down to demonstrate our knowledge of each step.

We create a result array, result, of length 2*len(nums). We then iterate through the integers in nums and populate result in just one pass using two pointers. The first pointer tracks the current location in nums and the second one adds a bias to allow for the repeated population.

Approach

1. Initialize result as a list of integers with length 2*len(nums)
2. Iterate through the length of nums while populating the same index, i, in result as well as the index len(nums) away which will have the repeated integer.
3. Return the result

Complexity

• Time complexity: $O(n)$. We iterate through the length of nums once which has linear time complexity.
• Space complexity: $O(n)$. We create a new list which takes 2*n space. $O(2*n) \rightarrow O(n)$.

Code

class Solution:
    def getConcatenation(self, nums: List[int]) -> List[int]:
        nums_length = len(nums)
        result = [0 for _ in range(nums_length * 2)]

        for i in range(nums_length):
            result[i] = nums[i]
            result[i + nums_length] = nums[i]
        
        return result