But in that top middle block only one cell can hold a 5. In that cell the numbers 4, 5, 6, and 8 are all possible. The dots in the cell in row 3, column 5, indicate that You should always start a Sudoku by finding all the hidden singles. Despite the name, hidden singles are far easier to find than naked singles. There is only one possible cell for a candidate. There is only one possible candidate for a cell a hidden single arises when This situation can arise for one of two reasons. When a candidate k is possible in only a single cell ofĪ row, column, or block, then that cell must be k. Hypothesis and proof and a sort of depth.Īll of these techniques are based on identifying all the possible "candidates" for a cell (indicated by marks)Īnd then eliminating them one by one until only one possibility remains in a given cell.Ĭross-Hatch Scanning (looking for singles) When all that fails, the Sudoku Assistant resorts to Almost-locked set analysis can be extended to grids, where itĪnd also to what I am calling almost-locked ranges. What I'm calling 3D Medusa analysis, includingĪnalysis. To learn more about my progress on the “Hard” Sudoku puzzle, read the full post of Sudoku Episode 3 here and keep your eyes peeled for part 4 of our series.The Sudoku Assistant uses several techniques to solve a Sudoku puzzle: If two cells in the same row, column, or box have the same pair of candidates, then both candidates can be removed from all other cells in the same row, column, or box… To put it another way, this new Sudoku rule is about candidate pairs. This means that in column 7 we can remove candidates 1 and 7 from the cells in rows 3 and 9. What we do know is that no other cell in that column can have 1 or 7 as candidates. This means one of them will have a value of 1 and the other will have a value of 7, but we don’t know which one is which just yet. Both cells have just two candidates: 1 and 7. The breakthrough was really on column seven, looking at the cells on the second and fifth rows. I then retraced my steps to understand what strategies I had applied. It wasn’t as easy as the medium puzzle, but after a few minutes, I started making some progress, scratching wrong candidates here and circling the right ones there, until the puzzle was complete. The picture below shows how far my set of five rules could progress.Īfter a couple of minutes of staring at the half-solved puzzle, I grabbed a pencil and started looking for a solution. And then I’ll get back to work.Īt the end of the previous episode, my attempt to solve a Hard Sudoku puzzle failed. It has been almost a year now since my fateful flight to Mexico when I first crossed paths with Sudoku and came up with the idea of using the optimized inference engine, along with a few other advanced features of FICO® Blaze Advisor®, to solve Sudoku puzzles. Ironically, the judge had previously complimented the jurors on the copious amounts of notes they were taking, before finding out what they were eagerly using their pencils for. The puzzles, management explained, were too distracting - a statement many found hard to argue against.Ī few years later, a district court judge in Australia had to discharge the jury on a three-month-long drug trial, after jurors were found to be playing Sudoku instead of listening to the evidence. In 2005 during the peak of the Sudoku craze, British Airways had to issue a memo to its flight attendants, forbidding them from playing Sudoku during takeoff and landing. But as with any type of addiction, it can also create its share of problems. Relief from depression, lowered blood pressure, and reduced anxiety have all been associated with the Sudoku habit. Sudoku is on a whole different level.įortunately for fellow Sudoku addicts across the globe, the Sudoku addiction is a vice with mostly beneficial side effects. iPhones and other such devices might be addictive. The Independent of London reported that a 700 percent increase in the sale of pencils has been attributed to the sudoku craze. “Hold my sake”, said Sudoku to the iPhone.
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