100x100 grid, spider walking and eating bugs
Source: IMOC 2021 C10
August 12, 2021
combinatorics
Problem Statement
In a by grid, there is a spider and bugs. Each time, the spider can walk up, down, left or right, and the spider aims to visit all the squares with bugs to eat them all. The spider begins from the top-left corner. Show that no matter where the bugs are, the spider can always eat them all within steps.