elizabeth_zou_fanboi's blog

By elizabeth_zou_fanboi, history, 5 hours ago, In English

a permutation is valid only if |ai — i| != k for all 1<=i<=n. Count the number of valid permutations.

Constraints: 2 ≤ N ≤ 2000

1 ≤ K ≤ N − 1

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