MathDB
Great Grid Combo

Source: RMM Shortlist 2023 C2

February 29, 2024
gridcolouringpathsright anglecombinatoricsRMM Shortlist

Problem Statement

For positive integers m,n2m,n \geq 2, let Sm,n={(i,j):i{1,2,,m},j{1,2,,n}}S_{m,n} = \{(i,j): i \in \{1,2,\ldots,m\}, j\in \{1,2,\ldots,n\}\} be a grid of mnmn lattice points on the coordinate plane. Determine all pairs (m,n)(m,n) for which there exists a simple polygon PP with vertices in Sm,nS_{m,n} such that all points in Sm,nS_{m,n} are on the boundary of PP, all interior angles of PP are either 9090^{\circ} or 270270^{\circ} and all side lengths of PP are 11 or 33.