# Competition #8: Sudoku (Internet searches)

Today’s competition is all about searching the Internet. You do not need to know how to solve Sudoku for this competition.

Sudoku uses a 9×9 grid with 81 cells. Starting with a grid with some cells already filled in with numbers, you have to complete the grid according to the rules using only the numbers 1 to 9. All Sudoku puzzles must have a unique solution.

The numbers initially filled in are called givens.  If there are originally 25 numbers, say, filled in before you start, you have 25 givens (numbers that you have already been given).

Many Sudoku puzzles have been found (i.e. uniquely solvable) that have 17 givens. No one knew if there was any Sudoku the existed with 16 givens. Computer searches were undertaken to find out if any Sudoku had 16 givens.

No Sudoku have been found with only 16 givens. A “proof” that none exist has been published.

Use the Internet to answer the questions below according to the rest of my rules.

Questions:

Q1. Approximately how many Sudoku have been found with 17 givens?

Q2. Find a more precise number of known Sudoku with 17 givens. You may have to look for a list of Sudoku with 17 givens.

Q3. Find a “Sudoku” with 16 givens that has only two solutions.

Q4. Who published the proof (give authors’ names) that there are no Sudoku with 16 givens? What date was this article published?

Q5. Many computer programs exist to solve a Sudoku. Find the code for a computer “program” (procedure) that is about five lines long or less. How long is the shortest known program?

Q6. If you have a Sudoku with 17 givens, how can you find out if a Sudoku exists with 16 givens within it? i.e. A Sudoku with 16 givens that has the 17th number (given) in its solution (same cell).

Good luck 🙂