Difference between revisions of "2017 USAMO Problems/Problem 2"

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==Problem==
  
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Let <math>m_1,\dotsc,m_n</math> be a collection of <math>n</math> positive integers, not necessarily distinct. For any sequence of integers <math>A = (a_1,\dotsc,a_n)</math> and any permutation <math>w_1,\dotsc,w_n</math> of  <math>m_1,\dotsc,m_n</math>, define an <math>A-inversion</math> of <math>w</math> to be a pair of entries <math>w_i,w_j</math> with <math>i<j</math> for which one of the following condition holds:

Revision as of 21:08, 27 November 2017

Problem

Let $m_1,\dotsc,m_n$ be a collection of $n$ positive integers, not necessarily distinct. For any sequence of integers $A = (a_1,\dotsc,a_n)$ and any permutation $w_1,\dotsc,w_n$ of $m_1,\dotsc,m_n$, define an $A-inversion$ of $w$ to be a pair of entries $w_i,w_j$ with $i<j$ for which one of the following condition holds: