Rewrite as four-dimensional route finding The grid isn't just a 2D grid. The constraints make it 4D: * X * Y * Last direction * Number of steps in that direction By tracking all four dimensions, we can find the shortest route for _all_ combinations of the constraint. Previously, we were dropping routes that were currently longer but ended up shorter because they could take subsequent steps that other routes couldn't.

--- Day 23: A Long Walk ---

You have a map made of blocked spaces (#), open spaces (.) and slopes (^, >, v, and <). You can't go back up slopes.

What is the LONGEST route from the start (open space in the top row) to the end (open space in the bottom row).