How many different ways are there to completely fill in the 81 squares of a Sudoku board? In May 2005, Felgenhauer and Jarvis counted the Sudoku boards carefully and concluded that there are exactly 6,670,903,752,021,072,936,960 solved boards. Mathematicians continue to play with and theorize about Latin squares today. But in 1959, a set of 10x10 "Euler's Spoiler" squares were discovered by Parker, Bose, and Shrikhande (in work popularized by Martin Gardner) disproving Euler's famous conjecture. His conjecture stood until the 20th century. Euler discovered that there did not seem to be very many Latin squares of a certain type, and in 1782 he proposed that the 36 Officers Problem had no solution for 6圆, 10x10, 14x14 squares, and so on. Solved Sudokus are a special kind of Latin square, which were studied by Euler. But with Sudokus, I wonder why they don't just let the software generate millions of puzzles? Imagine how many millions of puzzles "included" they could claim. With crosswords, I can understand why your software might have only a few hundred puzzles, since each hint needs to be done by a human editor. I guess it's no wonder that they recently came out with Sudoku for the Nintendo DS too.īut if you read the advertisements for Sudoku Gridmaster for DS, you will notice that it is said to come with " over 400" Sudoku puzzles. We brought a Dora Sudoku book on our trip to Taiwan, and solving Sudokus became the most reliably fun activity for Piper whenever she was waiting around, remarkably beating out her Nintendo DS. The amazing thing is that my pre-K daughter Piper was completely enthralled by the books. Since they are for the preliterate set, you fill in simplified 4x4 puzzles using stickers instead of letters or numbers. I realized Sudoku was a major phenomenon when I saw the Dora Sudoku books for preschoolers. There are many Sudoku variants, for example versions of the game where the 9-square blocks come in different shapes, or smaller versions of the game that are designed for children. (The best strategy in Sudoku is not to guess, yet it's still good to play with an erasable pencil.) It can also be fun to cooperate on a Sudoku puzzle - the entertainment there is to be stymied together, and then question the other person's clever move to get out of a logjam. You can be dealt a blow at the finish line when you encounter a contradiction and then realize you made a mistake long ago. Either player always has a chance to win a race, because backtracking in Sudoku is hard. Heidi and I sometimes race each other on adjacent puzzles in a Sudoku book - it can be nerve-wracking to try to catch up when you're behind, while the other person is rapidly filling in squares. Sudoku is a good solo game if you are having trouble getting into it, you can read about various solution strategies on the web.īut, like crosswords, it can be even more fun to work Sudoku puzzles together with somebody else. Puzzles are designed so that there is only one correct way to fill in the 81 squares, and they tend to be just hard enough to be satisfying: not too easy, not impossible. The rules of Sudoku are simple: finish filling in the squares of a 9x9 grid so that the digits 1-9 appear exactly once in each of the nine rows, columns, and 3x3 blocks. Have you ever played Sudoku? A few months ago my dad raved about a new game in the newspaper that he liked solving better than the daily crossword, and so I picked up one of the five hundred or so Sudoku books at the bookstore. Update: For Google Chrome users, try installing this Chrome Sudoku Web App for hints and more. It is a nice example of the website fun you can have with 250 lines of Python over a Labor day weekend it also makes a handy command-line Sudoku solver. Here is a free Sudoku generator that can generate puzzles of varying difficulty in PDF, Postscript, plaintext, and HTML.
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