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A regular crossword
» Home : Blog : February 2013
A friend shared a link to an unusual puzzle (click for a full-page PDF):
Each row has a regular expression indicating the letters to fill the row. Each cell is at the intersection of three rows, so there are a number of constraints to satisfy at each point.
Overlapping constraints are a good basis for logic puzzles. Sudoku, Ken-Ken, Nonograms, and plenty of other puzzle forms follow the same recipe: determine the contents of a cell, based on multiple simultaneous constraints.
But the regexes here add an extra dimension. Each of the regexes here has a different form, resulting in different levels of information. Two rows have .*, or no information at all. Another has [CR]*, so we know the entire row is C's and R's. Each row has a different regex, so the interaction is varied across the grid.
I wrote to the author, Dan Gulotta, about how he constructed it, and he told me,
A few times during my solving of the puzzle, I used the classic piece of puzzle meta-information as part of the deduction: there is a unique solution. A friend of mine said he solved it without using that fact, but I don't see a reason to avoid it.
By the way, I didn't realize this when I solved it, but there's another level to the puzzle, which is to identify the phrase in it. It was part of the 2013 MIT Mystery Hunt.