Question 2
The Planar National Park is an undirected 3-regular planar graph: every vertex has degree three. A visitor starts at a vertex along an edge, then turns left at the next vertex, right at the following vertex, and alternates left and right thereafter. She stops on returning to her starting vertex. Over all park layouts, what is the largest number of times she could have entered a vertex?
Proposed by Zoran Sunic. Evan Chen’s third-party solution notes: https://aops.com/community/p21498640; source video https://youtu.be/9WNgDETHOlI?t=1325. One point is nonofficial editorial normalization; manual essay grading only.
Proposed by Zoran Sunic. Evan Chen’s third-party solution notes: https://aops.com/community/p21498640; source video https://youtu.be/9WNgDETHOlI?t=1325. One point is nonofficial editorial normalization; manual essay grading only.