Problem of the Week 1140

You Are a Train

This diagram shows a railway maze, where one seeks a path along the tracks from A to B that could be followed by a train:

At each junction, the train must follow the curve of the track. And the train cannot go in reverse: the wheels can only turn in the forward direction.

There is a unique solution. Find it.

Source: Maze is by Lionel Penrose and Roger Penrose, 1958. See Roger Penrose, "Railway mazes," in A Lifetime of Puzzles, E. D. Demaine, M. L. Demaine, T. Rodgers, eds., AK Peters, Wellesley, Mass., 2008, 133-148.

© Copyright 2011 Stan Wagon. Reproduced with permission.