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About Sudoku
  Sudoku, or Su Doku is a type of puzzle where a 9x9 grid of squares contains the numbers 1-9, one in each grid cell, where a number can not be repeated in any row, column or box (boxes are delineated by thicker lines). Thus, each row, column and box must have exactly one of each digit between 1 and 9. Other variations of Sudoku exist, such as 4x4 grids and 16x16 grids, and numbers can be replaced with letters or colors, but this version of Sudoku Snake does not explore those variations.

  Each Sudoku puzzle begins with a certain number of given values. There are usually 20-30 givens. It is often believed that the more givens there are, the easier the puzzle will be. This is not quite the case. The most important factor is the patterns created by the givens and the difficulty of solving techniques required to solve the puzzle.

  There are many solving techniques that have been discovered and may yet be discovered to solve Sudoku puzzles. Click here for a complete list of the techniques employed by Sudoku Snake. Refer to this list to learn tricks and tips for solving these puzzles. There is no tutorial better than researching solving techniques and practicing spotting them.

  To be a valid Sudoku puzzle, there must be only one possible solution, or unique solution. Sudoku Snake automatically checks to see if at any time a puzzle has one unique solution, multiple possible solutions, or no solution at all. If a puzzle has multiple solutions, then guess-and-check techniques must be employed to find a solution. Sudoku Snake does not use guess-and-check methods or methods that are based on the assumption that a puzzle has a unique solution (such as Unique Rectangles, BUGs, or Nishio) when computing skill levels or offering hints. Puzzles with no solution will create contradictions when trying to use logical methods, and puzzles with a unique solution can be solved using logical methods alone.

  Some logical techniques are beyond the ability for human solvers to spot, at least within a reasonable amount of time. Dynamic Nested Forcing Chains II is one example. Sudoku Snake has created a skill rating system to help gauge which puzzles should be attempted by people of varying skill with Sudoku. There is no universally accepted rating system for Sudoku puzzles. In fact, there are hundreds of systems out there. Sudoku Snake has created its own, described here, that is based off of points awarded for passes of solving techniques. Then, once the solution is achieved, the skill level is the natural log of the number of points awarded. Each technique gives a different number of points, as seen on each page describing a solving technique.

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