Difference between revisions of "2023 USAJMO Problems/Problem 3"

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==Problem==
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Consider an <math>n</math>-by-<math>n</math> board of unit squares for some odd positive integer <math>n</math>. We say that a collection <math>C</math> of identical dominoes is a maximal grid-aligned configuration on the board if <math>C</math> consists of <math>(n^2-1)/2</math> dominoes where each domino covers exactly two neighboring squares and the dominoes don't overlap: <math>C</math> then covers all but one square on the board. We are allowed to slide (but not rotate) a domino on the board to cover the uncovered square, resulting in a new maximal grid-aligned configuration with another square uncovered. Let <math>k(C)</math> be the number of distinct maximal grid-aligned configurations obtainable from <math>C</math> by repeatedly sliding dominoes. Find the maximum value of <math>k(C)</math> as a function of <math>n</math>.

Revision as of 15:43, 8 May 2023

Problem

Consider an $n$-by-$n$ board of unit squares for some odd positive integer $n$. We say that a collection $C$ of identical dominoes is a maximal grid-aligned configuration on the board if $C$ consists of $(n^2-1)/2$ dominoes where each domino covers exactly two neighboring squares and the dominoes don't overlap: $C$ then covers all but one square on the board. We are allowed to slide (but not rotate) a domino on the board to cover the uncovered square, resulting in a new maximal grid-aligned configuration with another square uncovered. Let $k(C)$ be the number of distinct maximal grid-aligned configurations obtainable from $C$ by repeatedly sliding dominoes. Find the maximum value of $k(C)$ as a function of $n$.