Build an array using the integers from 1 through n. The value 1 appears once, and every value k from 2 through n appears twice. The two copies of k must occupy indices whose difference is exactly k. Return the lexicographically largest valid array: at the first position where two arrays differ, prefer the one with the larger value. The array has length 2*n-1, and a valid answer always exists.
Example 1:
Input: n = 1
Output: [1]Explanation: Only the value 1 is available, and it appears once. The sole valid array is [1].
Example 2:
Input: n = 2
Output: [2,1,2]Explanation: The two copies of 2 occupy indices 0 and 2, whose difference is 2. The remaining position holds 1, yielding [2,1,2].
Example 3:
Input: n = 4
Output: [4,2,3,2,4,3,1]Explanation: In [4,2,3,2,4,3,1], the copies of 4 are four positions apart, the copies of 3 are three apart, and the copies of 2 are two apart. Starting with 4 and then 3 cannot be completed legally; starting with 4 and then 2 gives this largest valid array.
Constraints:
1 <= n <= 20