Concatenation of Array — C++

// Time:  O(n)
// Space: O(1)

class Solution {
public:
    vector<int> getConcatenation(vector<int>& nums) {
        int n = size(nums);
        nums.resize(2 * n);
        for (int i = 0; i < n; ++i) {
            nums[n + i] = nums[i];
        }
        return nums;
    }
};