Checkered square
Source: 239 2008 J5
July 28, 2020
combinatorics
Problem Statement
You are given a checkered square, the side of which is long and contains nodes. A non-return path is a path along edges, the intersection of which with any horizontal or vertical line is a segment, point or empty set, and which does not pass along any edge more than once. What is the smallest number of non-return paths that can cover all the edges?
(An edge is a unit segment between adjacent nodes.)