Advanced and Full-Featured: Sudoku4ever
Sudoku4ever by 1gravity offers an unlimited number of puzzles, eight difficulty levels from Very Easy to Nightmare, a world-class hint engine, game statistics and global high scores.
A standard Sudoku puzzle consists of a 9×9 grid, with a total of 81 cells. Each position in the grid is called a cell. A cell can be empty, or filled with a digit. This digit can be any digit between one and nine. You must place digits into the grid in such a way that every row, every column, and every 3×3 box contains each of the digits one through nine.
A number of digits have been placed into the grid by the maker. They are called givens, clues, or fixed digits. They are placed in such a way that you can use logical reasoning to find the solution. A well-formed Sudoku has a single solution that can be found by reasoning, regardless of the complexity of that reasoning.
Sudoku: A Brief History
A game called “Number Place” was designed by Howard Garns, and first published by Dell Magazines in 1979. The puzzle was introduced in Japan by Nikoli in 1984, who gave it the name “Sudoku,” which is an abbreviation for the original Japanese name meaning “The Numbers must be Unique.” The whole world adopted this new name, but in Japan, Nikoli owns the trademark, so other publishers in Japan call it Nanpure, the Japanese translation of Number Place.
By the end of 2004, Sudoku appeared in The Times in Britain, brought to Europe by Wayne Gould, the founder of Pappocom. Many newspapers worldwide followed. Sudoku magazines can be found everywhere. Sudokus are published on the Internet on a daily basis. And many people have become addicted to it.
Every puzzle included in Sudoku4ever has a unique solution and can be solved using logic only (no guessing), although there’s a controversial discussion going on in the Sudoku community about where logic ends and guessing starts, and which solving technique belongs to which category. If you doubt that a puzzle is solvable, use the solve function (the solver also checks for multiple solutions) or the hint function to get a step-by-step solution path.
For aesthetic reasons, a large part of Sudoku puzzle makers think they look nicer by making them symmetric one way or the other. From a mathematical point of view, the symmetry has no effect, other than that the chances for redundant givens in the grid increases with a higher level of symmetry. Sudoku4ever generates symmetrical puzzles only.