Codeforces Round 836 (Div. 2) |
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Finished |
Given two integers $$$n$$$ and $$$x$$$, a permutation$$$^{\dagger}$$$ $$$p$$$ of length $$$n$$$ is called funny if $$$p_i$$$ is a multiple of $$$i$$$ for all $$$1 \leq i \leq n - 1$$$, $$$p_n = 1$$$, and $$$p_1 = x$$$.
Find the lexicographically minimal$$$^{\ddagger}$$$ funny permutation, or report that no such permutation exists.
$$$^{\dagger}$$$ A permutation of length $$$n$$$ is an array consisting of each of the integers from $$$1$$$ to $$$n$$$ exactly once.
$$$^{\ddagger}$$$ Let $$$a$$$ and $$$b$$$ be permutations of length $$$n$$$. Then $$$a$$$ is lexicographically smaller than $$$b$$$ if in the first position $$$i$$$ where $$$a$$$ and $$$b$$$ differ, $$$a_i < b_i$$$. A permutation is lexicographically minimal if it is lexicographically smaller than all other permutations.
The input consists of multiple test cases. The first line contains an integer $$$t$$$ ($$$1 \leq t \leq 10^4$$$) — the number of test cases. The description of the test cases follows.
The only line of each test case contains two integers $$$n$$$ and $$$x$$$ ($$$2 \leq n \leq 2 \cdot 10^5$$$; $$$1 < x \leq n$$$).
The sum of $$$n$$$ across all test cases does not exceed $$$2 \cdot 10^5$$$.
For each test case, if the answer exists, output $$$n$$$ distinct integers $$$p_1, p_2, \dots, p_n$$$ ($$$1 \leq p_i \leq n$$$) — the lexicographically minimal funny permutation $$$p$$$. Otherwise, output $$$-1$$$.
33 34 25 4
3 2 1 2 4 3 1 -1
In the first test case, the permutation $$$[3,2,1]$$$ satisfies all the conditions: $$$p_1=3$$$, $$$p_3=1$$$, and:
In the second test case, the permutation $$$[2,4,3,1]$$$ satisfies all the conditions: $$$p_1=2$$$, $$$p_4=1$$$, and:
We can show that these permutations are lexicographically minimal.
No such permutations exist in the third test case.
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