The fewest clues required for a proper Sudoku is 17, but not all completed grids can be reduced to a proper 17 clue Sudoku. About 49,000 unique (non-equivalent) Sudokus with 17 clues have been found. (A proper Sudoku has only one solution).
What is the minimal number of clues in a valid puzzle?
17 clues
Puzzles must have at least 17 clues to have a valid solution.
Do all Sudoku puzzles have a unique solution?
The short answer is yes! There is no rule that requires Sudokus to have a unique solution. This is because in these Sudoku puzzles there cannot be a clue for every digit from 1 to 9 in the initial clue. In other words, there must be at least two digits that do not appear in any clue.
Is doing Sudoku good for your brain?
Sudoku is a great game to help improve memory. A lot of online Sudoku daily puzzles are timed, which also helps. When you have to remember how to do something in a set amount of time it can help improve your memory. It works almost like a memory match game.
How many clues do you need to solve a Sudoku puzzle?
It has been conjectured for some time that 17 clues is the minimum number of necessary clues to make a single solution Sudoku puzzle. There are about 50,000 such puzzles collected from various sources out and about on the Internet. One such set I use for calibrating and testing.
What makes a Sudoku different from a normal Sudoku?
Ordinary Sudokus (proper puzzles) have a unique solution. A minimal Sudoku is a Sudoku from which no clue can be removed leaving it a proper Sudoku. Different minimal Sudokus can have a different number of clues.
How many Sudoku boards are there in the world?
First you must obtain (or generate) all possible unique filled-in Sudoku boards, of which there are 5,472,730,538. The algorithm must also take into account higher order Avoidable Sets (with nine numbers instead of 4). So it is understandable that the computing time was still considerable.
Is the 9×9 Sudoku puzzle made of square nonominoes?
The classic 9×9 Sudoku is made of square nonominoes. It is possible to apply the rules of Sudoku to puzzles of other sizes, although only N2 × N2 Sudoku puzzles can be tiled with square polyominoes. See the Glossary of Sudoku for an expanded list of variants.
