All 48 states with no repeats
The statics-about-news site FiveThirtyEight features a riddle or puzzle every Friday. Last Friday, the challenge was to find a path through the lower 48 states that visited all with no repeats. This is based only on crossing borders, not taking roads, and in that light at least it can be done. It can be visualized by treating each state as a vertex and each border as a line.
One respondent claimed to have made a path that crosses 91 borders without any repeat crossings, but he treated Four Corners incorrectly, I'd allege
https://fivethirtyeight.com/features...ircular-train/
(scroll down for "Solution To Last Week's Riddler Classic")
...Still haven't seen anyone visiting all the places in "I've Been Everywhere" in order, not the US nor the Australian version. Maybe when I'm old...
One respondent claimed to have made a path that crosses 91 borders without any repeat crossings, but he treated Four Corners incorrectly, I'd allege
https://fivethirtyeight.com/features...ircular-train/
(scroll down for "Solution To Last Week's Riddler Classic")
...Still haven't seen anyone visiting all the places in "I've Been Everywhere" in order, not the US nor the Australian version. Maybe when I'm old...