Swiss crosses insides a 7x7 square, divided into unit squares
Source: Switzerland - Swiss TST 2002 p4
February 18, 2020
combinatorial geometrycombinatorics
Problem Statement
A square is divided into unit squares by lines parallel to its sides. Some Swiss crosses (obtained by removing corner unit squares from a square of side ) are to be put on the large square, with the edges along division lines. Find the smallest number of unit squares that need to be marked in such a way that every cross covers at least one marked square.