1929. Concatenation of Array - Explanation

Problem Link

Description

You are given an integer array nums of length n. Create an array ans of length 2n where ans[i] == nums[i] and ans[i + n] == nums[i] for 0 <= i < n (0-indexed).

Specifically, ans is the concatenation of two nums arrays.

Return the array ans.

Example 1:

Input: nums = [1,4,1,2]

Output: [1,4,1,2,1,4,1,2]

Example 2:

Input: nums = [22,21,20,1]

Output: [22,21,20,1,22,21,20,1]

Constraints:

• 1 <= nums.length <= 1000.
• 1 <= nums[i] <= 1000

Company Tags

Please upgrade to NeetCode Pro to view company tags.

1. Iteration (Two Pass)

class Solution:
    def getConcatenation(self, nums: List[int]) -> List[int]:
        ans = []
        for i in range(2):
            for num in nums:
                ans.append(num)
        return ans

Time & Space Complexity

• Time complexity: $O(n)$
• Space complexity: $O(n)$ for the output array.

---

2. Iteration (One Pass)

class Solution:
    def getConcatenation(self, nums: List[int]) -> List[int]:
        n = len(nums)
        ans = [0] * (2 * n)
        for i, num in enumerate(nums):
            ans[i] = ans[i + n] = num
        return ans

Time & Space Complexity

• Time complexity: $O(n)$
• Space complexity: $O(n)$ for the output array.