CF1816B.Grid Reconstruction

Consider a $2 \times n$ grid, where $n$ is an even integer. You may place the integers $1, 2, \ldots, 2n$ on the grid, using each integer exactly once.

A path is a sequence of cells achieved by starting at $(1, 1)$ , then repeatedly walking either downwards or to the right, and stopping when $(2, n)$ is reached. The path should not extend beyond the grid.

The cost of a path is the alternating sum of the numbers written on the cells in a path. That is, let the numbers written on the cells be $a_1, a_2, \ldots, a_k$ (in the order that it is visited), the cost of the path is $a_1 - a_2 + a_3 - a_4 + \ldots = \sum_{i=1}^k a_i \cdot (-1)^{i+1}$ .

Construct a way to place the integers $1, 2, \ldots, 2n$ on the grid, such that the minimum cost over all paths from $(1, 1)$ to $(2, n)$ is maximized. If there are multiple such grids that result in the maximum value, output any of them.

The first line contains a single integer $t$ ( $1 \leq t \leq 1000$ ) — the number of test cases. The description of test cases follows.

The first and the only line of each test case contains a single integer $n$ ( $2 \leq n \leq 10^5$ , $n$ is even) — the number of the columns in the grid.

It is guaranteed that the sum of $n$ over all test cases does not exceed $10^5$ .

For each test case, output $2$ lines, each containing $n$ integers — the desired grid. If there are multiple solutions, output any of them.

In the first test case, there are only two paths from cell $(1, 1)$ to cell $(2, 2)$ . Their costs are $3-1+4=6$ and $3-2+4=5$ . Then the minimum cost is $5$ , which is the maximum possible value.

In the second test case, there are four paths from cell $(1, 1)$ to cell $(2, 4)$ . Their costs are $8-1+5-3+7=16$ , $8-2+5-3+7=15$ , $8-2+6-3+7=16$ , and $8-2+6-4+7=15$ . Then the minimum value is $15$ , which is the maximum possible value.