Broken Sign Blog
#165: U-Bahn (Embedded Latin Square)
25 April 2025This puzzle was submitted to Logic Showcase 68: It’s Not Hip To Be Square. The prompt was to make puzzles that are sort of Latin Squares, but not quite, e.g. partial Latin Squares, non-square grids, non-digit/letter banks, etc.
I don’t have much else to add to this puzzle. It’s pretty tough, but it’s got some nice logic.
Rules: Draw a continuous subway map into the diagram that runs horizontally and vertically from cell centre to cell centre and does not leave the diagram anywhere. The lines can branch or turn at the cell centres, but there are no dead ends. The numbers at the edge indicate how many of the corresponding segments occur in the corresponding row or column. The segments may also be rotated.
Variant: Within the shaded area, each type of segment occurs exactly once in each row and column.