Kanata18's blog

Combinatorics problem
By Kanata18, history, 5 hours ago, In English

Hello codeforces community!!

On this occasion I bring up a combinatorics problem.

This is the problem:

How many permutations of length N exist such that the following holds: for each i (1 <= i < N) p[i+1] — p[i] != 1

Constants: 1 <= N <= 500

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5 hours ago, # |
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Auto comment: topic has been updated by Kanata18 (previous revision, new revision, compare).

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3 hours ago, # |
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I haven't proved my solution yet, but this should solve the task in $$$\mathcal{O}(n)$$$.

Solution
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3 hours ago, # |
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It occurred to me to do it using: Connected Component DP (although I don't know how to implement it)

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10 minutes ago, # |
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This problem is the exact same as CSES — Permutations II, although the constraints are $$$n \leq 5000$$$.

Note, this task could be solved in $$$O(n)$$$, you can check it on USACO Guide — Solution

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5 minutes ago, # |
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Thank you very much for the material

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