Path Puzzles Font 
by Jeffrey Bosboom, Erik Demaine, Martin Demaine, Adam Hesterberg, Roderick Kimball, and Justin Kopinsky, 2020 


Path puzzles are a type of pencilandpaper logic puzzle introduced by Roderick Kimball in 2013 and featured in The New York Times's Wordplay blog in 2014. In its simplest form, a puzzle consists of a grid of cells with two “doors” on the boundary, and numerical constraints on some of the rows and columns. The goal is to draw one noncrossing path between the two boundary doors so that the number of cells visited in each constrained row or column matches the specified number (if any). Like most pencilandpaper logic puzzles, path puzzles are NPcomplete, meaning that there is no efficient algorithm to solve them, assuming P ≠ NP.
This typeface features 26 uniquely solvable 6 × 6 path puzzles, one for each letter of the alphabet. In the solved font, the paths form the letter shapes. In the puzzle font, you can interactively solve the puzzle by clicking on grid edges to toggle whether they are part of the solution path. If you Enable third “wall” state, then you can click on an edge a second time to make it a wall, indicating that the path can't go there. Right clicking acts as an eraser. Middle clicking draws with walls if they are enabled. You can drag (slowly) to paint many edges or walls at once. If you connect more than two edges at any vertex, they will highlight red. As mentioned in our paper, we verified by exhaustive search that each of these puzzles has a unique solution.
Check out other mathematical and puzzle fonts. • Feedback or not working? Email Erik. • Source code on GitHub.