MathDB
Lattice Point Connections

Source:

August 8, 2024
combinatorics2022

Problem Statement

Let Λ\Lambda denote the set of points (x,y)(x,y) in 2D space with integer coordinates such that 0x40\leq x\leq 4 and 0y20\leq y\leq 2. That is, Λ={(x,y)Z2:0x4, 0y2}. \Lambda=\{ (x,y) \in \mathbb{Z}^2: 0\leq x\leq 4, \ 0\leq y\leq 2 \}. Find the number of ways to connect points of Λ\Lambda with segments of length 2\sqrt{2} or 5\sqrt{5} such that the interior of any unit square with vertices in Λ\Lambda contains part of exactly one segment; an example is shown below (connections that differ by reflections are distinct). [asy] unitsize(1cm); dot((0,0)); dot((1,0)); dot((2,0)); dot((3,0)); dot((4,0)); dot((0,1)); dot((1,1)); dot((2,1)); dot((3,1)); dot((4,1)); dot((0,2)); dot((1,2)); dot((2,2)); dot((3,2)); dot((4,2)); draw((0,0)--(1,1)); draw((0,2)--(2,1)); draw((1,1)--(2,0)); draw((2,0)--(3,2)); draw((3,1)--(4,2)); draw((3,0)--(4,1)); [/asy]