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combinatorial game!!! CMO 2015 P3

Source: canadian mathematical olympiad

April 24, 2015
combinatoricssquare grid

Problem Statement

On a (4n+2)×(4n+2)(4n + 2)\times (4n + 2) square grid, a turtle can move between squares sharing a side.The turtle begins in a corner square of the grid and enters each square exactly once, ending in the square where she started. In terms of nn, what is the largest positive integer kk such that there must be a row or column that the turtle has entered at least kk distinct times?