Codeforces Round 992 (Div. 2) |
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Finished |
Consider a permutation$$$^{\text{∗}}$$$ $$$p_1, p_2, \ldots, p_n$$$ of integers from $$$1$$$ to $$$n$$$. We can introduce the following sum for it$$$^{\text{†}}$$$:
$$$$$$S(p) = \sum_{1 \le l \le r \le n} \min(p_l, p_{l + 1}, \ldots, p_r)$$$$$$
Let us consider all permutations of length $$$n$$$ with the maximum possible value of $$$S(p)$$$. Output the $$$k$$$-th of them in lexicographical$$$^{\text{‡}}$$$order, or report that there are less than $$$k$$$ of them.
$$$^{\text{∗}}$$$A permutation of length $$$n$$$ is an array consisting of $$$n$$$ distinct integers from $$$1$$$ to $$$n$$$ in arbitrary order. For example, $$$[2,3,1,5,4]$$$ is a permutation, but $$$[1,2,2]$$$ is not a permutation ($$$2$$$ appears twice in the array), and $$$[1,3,4]$$$ is also not a permutation ($$$n=3$$$ but there is $$$4$$$ in the array).
$$$^{\text{†}}$$$For example:
$$$^{\text{‡}}$$$An array $$$a$$$ is lexicographically smaller than an array $$$b$$$ if and only if one of the following holds:
Each test contains multiple test cases. The first line contains the number of test cases $$$t$$$ ($$$1 \le t \le 10^4$$$). The description of the test cases follows.
The only line of each test case contains two integers $$$n$$$ and $$$k$$$ ($$$1 \le n \le 2 \cdot 10^5$$$; $$$1 \le k \le 10^{12}$$$) — the length of the permutation and the index number of the desired permutation.
It is guaranteed that the sum of $$$n$$$ over all test cases does not exceed $$$2 \cdot 10 ^ 5$$$.
For each test case, if there are less than $$$k$$$ suitable permutations, print $$$-1$$$.
Otherwise, print the $$$k$$$-th suitable permutation.
63 23 34 114 66 397 34
1 3 2 2 3 1 -1 2 4 3 1 -1 2 3 4 5 7 6 1
Let us calculate the required sum for all permutations of length $$$3$$$ (ordered lexicographically):
Permutation | Value of $$$S(p)$$$ |
$$$[1, 2, 3]$$$ | $$$10$$$ |
$$$[1, 3, 2]$$$ | $$$10$$$ |
$$$[2, 1, 3]$$$ | $$$9$$$ |
$$$[2, 3, 1]$$$ | $$$10$$$ |
$$$[3, 1, 2]$$$ | $$$9$$$ |
$$$[3, 2, 1]$$$ | $$$10$$$ |
In the first test case, you have to print the second suitable permutation of length $$$3$$$. Looking at the table, we see that it is the permutation $$$[1, 3, 2]$$$.
In the second test case, you have to print the third suitable permutation of length $$$3$$$. Looking at the table, we see that it is the permutation $$$[2, 3, 1]$$$.
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