Problem Description

Given a integer array nums of length n, create a new array ans of length 2 * n that satisfies the following conditions for all indices 0 ≤ i < n:

• ans[i] equals nums[i]
• ans[i + n] equals nums[i]

In other words, the resulting array ans is formed by concatenating two copies of the original nums array.

Constraints

• n = nums.length
• 1 ≤ n ≤ 1000
• 1 ≤ nums[i] ≤ 1000

Examples

Example 1:

Input: nums = [1, 2, 1]
Output: [1, 2, 1, 1, 2, 1]
Explanation: The answer array is formed as:
ans = [nums[0], nums[1], nums[2], nums[0], nums[1], nums[2]]
ans = [1, 2, 1, 1, 2, 1]

Example 2:

Input: nums = [1, 3, 2, 1]
Output: [1, 3, 2, 1, 1, 3, 2, 1]
Explanation: The answer array is formed as:
ans = [nums[0], nums[1], nums[2], nums[3], nums[0], nums[1], nums[2], nums[3]]
ans = [1, 3, 2, 1, 1, 3, 2, 1]

Solution Approach

This problem has a straightforward solution. Since we need to create an array that conssits of two copies of the input array placed end-to-end, we can simply use array concatenation. The operation nums + nums in Python creates a new list by appenidng a copy of nums to itself.

The time complexity is O(n) since we need to copy all n elements twice, and the space complexity is O(n) for storing the resulting array.

Reference Implementation

def concatenate_arrays(source: list) -> list:
    """Return a new array containing two concatenated copies of the input."""
    return source + source


def main():
    """Read input and display the concatenated array."""
    raw_input = input("Enter integers separated by spaces: ")
    numbers = list(map(int, raw_input.split()))
    
    result = concatenate_arrays(numbers)
    print("Concatenated array:", result)


if __name__ == "__main__":
    main()