HBC52166取钱,二分,分治Inversions of all permutations题解

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Amy asks Mr. B problem C. Please help Mr. B to solve the following problem. Given an array aiwith length n, and a base b. For each permutation {ri} of {ai}, we count the number of inversions as t. Please calculate ∑{ri}isapermutationof{ai}btsum_{{r_i} text{is a permutation of} {a_i}} b^{t}∑{ri}isapermutationof{ai}bt As the answer might be very large, please output it modulo 1000000007.

Amy asks Mr. B  problem C. Please help Mr. B to solve the following problem. Given an array ai with length n, and a base b. For each permutation {ri} of {ai}, we count the number of inversions as t({ri}). Please calculate ∑{ri}is a permutation of{ai}bt({ri})sum_{{r_i} text{is a permutation of} {a_i}} b^{t({r_i})}∑{ri​}is a permutation of{ai​}​bt({ri​}) As the answer might be very large, please output it modulo 1000000007.

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标签： HBC52166取钱 二分 分治Inversions of all permutations题解