Is Concatenate Array With Reverse easy or hard?

Concatenate Array With Reverse is considered an Easy problem. It focuses on understanding array indexing and reversing logic rather than complex algorithms or data structures.

Concatenate Array With Reverse Python/Java solution

In Python, you can build the result with nums + nums[::-1] or by filling a preallocated list using index calculations. In Java, create an int array of size 2*n and assign result[i] = nums[i] and result[2*n-1-i] = nums[i] inside a loop.

How to solve Concatenate Array With Reverse in O(n)?

Allocate a result array with length twice the input size. Iterate from i = 0 to n-1, assign result[i] = nums[i] and result[2n - 1 - i] = nums[i]. This fills the original and reversed parts simultaneously using one linear traversal.

What is the best approach for Concatenate Array With Reverse?

The best approach constructs the result array in a single pass. Allocate an array of size 2n and fill the first half with nums[i] while placing the same value at index 2n-1-i for the reverse portion. This avoids building a separate reversed array and runs in O(n) time with O(n) space.

Is Concatenate Array With Reverse asked at Google/Amazon/Meta?

This exact problem is categorized as an Easy array manipulation question. While the exact wording may not appear in major interviews, similar tasks involving reversing arrays, constructing mirrored arrays, or handling index symmetry appear frequently in coding screens.

What data structure is used in Concatenate Array With Reverse?

The problem relies on basic array operations. The solution typically uses a new array of size 2n to store the original sequence followed by its reversed order. No advanced data structures are required.

What is the time complexity of Concatenate Array With Reverse?

The optimal solution runs in O(n) time because each element of the input array is processed exactly once. A result array of size 2n must be created, so the auxiliary space complexity is O(n).

Description Solution Video 5:42

3925. Concatenate Array With Reverse

Easy91.1% acceptance

You are given an integer array nums of length n.

Construct a new array ans of length 2 * n such that the first n elements are the same as nums, and the next n elements are the elements of nums in reverse order.

Formally, for 0 <= i <= n - 1:

ans[i] = nums[i]
ans[i + n] = nums[n - i - 1]

Return an integer array ans.

Example 1:

Input: nums = [1,2,3]

Output: [1,2,3,3,2,1]

Explanation:

The first n elements of ans are the same as nums.

For the next n = 3 elements, each element is taken from nums in reverse order:

ans[3] = nums[2] = 3
ans[4] = nums[1] = 2
ans[5] = nums[0] = 1

Thus, ans = [1, 2, 3, 3, 2, 1].

Example 2:

Input: nums = [1]

Output: [1,1]

Explanation:

The array remains the same when reversed. Thus, ans = [1, 1].

Constraints:

1 <= nums.length <= 100
1 <= nums[i] <= 100

Topics

Array Simulation

5:42

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1class Solution:
2    def concatWithReverse(self, nums: list[int]) -> list[int]:
3        

Starter codePython 3Spaces: 4

Examples

Case 1Case 2

Input

[1,2,3]

Input

[1]

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