So another week and some more WSC stuff to present. A very basic outline of the individual competition is now available online; listed on it is one of the big new projects we've been working on. If Tablecloth Sudoku was the puzzle style that Wei-Hwa and I created at the second WSC, Just One Cell Sudoku is the puzzle that the two of us created at the fourth "WSC", just after the Guinness Record round lunacy. Let me frame the concept in the way I see it first.
Chess Puzzles:Chess::Just One Cell Sudoku:Sudoku
Chess is a game of strategy played between two individuals. However, outside of any individual game, there is an established body of interesting game situations or strategies that can be presented as "puzzles" to someone familiar with Chess to test their powers of deduction and perhaps teach or expand the strategies they can recognize at a given board setting. I wrote several of them for GAMES Puzzlecraft #50 (April 2009), which taught me amongst other things how much I still have to learn about Chess.
Sudoku is a Latin Square-based constraint-satisfaction puzzle with a single solution but multiple cells to fill in to get to that solution. However, outside of any individual grid, there is an established body of solving strategies which can be presented as "puzzles" to someone familiar with sudoku to test their powers of deduction and perhaps teach or expand the strategies they can recognize at a given grid position. I wrote over two dozen of them for the WSC, which taught me amongst other things how few solving strategies I actually use when I'm solving at my fastest.
The hardest sudoku puzzles at a competition are almost always solved for speed using bifurcation and not logic by the best solvers. It is the dirty little secret I freely admit but one that leaves my performance on some puzzles much less satisfying than others. I won the Classic Sudoku title in Goa by guessing on an impossibly difficult puzzle ("Goes to 11") after having an edge in classics on three earlier, much much much more solvable puzzles. I won the overall Sudoku title in Goa by simply solving all of the puzzles very fast using logic, not bifurcation. Only one of the two titles matters a lot to me.
"Goes to 11" and the Guinness puzzle last year are obvious examples of competition "sudoku" where logic ISN'T EVEN POSSIBLE! for a human within the intended time constraints after a very small number of cells. This showcases a general problem with a potential goal of a sudoku competition to identify those solvers who have learned and can use the "fiendish-level" strategies. Sometimes it is not speed that impresses, but the depth of one's wisdom. Just One Cell Sudoku are meant to assess the latter by isolating single "sticking points" in the solving process that require various kinds of observations.
Rules: In Just One Cell Sudoku, each of the puzzles has multiple solutions for the entire grid but has an unfilled cell that is "fixed" in all of the possible solutions. Using standard/advanced solving strategies, identify this single cell that can be specified. For more advanced strategies, candidates will be given in the grids to assist in identifying the necessary deduction.