9x9 Evil Sudoku

About Sudoku Puzzles

Sudoku is a logic-based, popular number-placement puzzle. The classic Sudoku grid consists of a 9×9 board divided into nine 3×3 sub-grids called "boxes" or "regions." The goal is to fill the grid with digits from 1 to 9 so that each digit appears exactly once in each row, column, and box.

Sudoku puzzles vary in difficulty, ranging from easy to expert, depending on how many digits are pre-filled and the complexity of solving them.

Basic Rules / How to Play

• Grid Size: The puzzle has 9x9 grid size made up of nine 3x3 sub-grids.
• Unique Numbers: Each row, column, and sub-grid must contain all digits from 1 to 9 without repetition.
• Pre-Filled Numbers: The numbers given at the start of the puzzle must remain unchanged.

Solving Tips and Techniques:

• Most Pre-filled Numbers: Start with rows, columns, or boxes with the most pre-filled numbers.
• Scanning: Look for empty cells where only one number is possible based on the existing numbers in the row, column, and subgrid.
• Elimination: If a number can only go into one cell in a row, column, or box, place it there.
• Single Candidates: A cell that can only have one number is filled right away.
• Candidate Lists: Write all the possible numbers in each empty cell. As you fill in numbers, remove the ones that no longer work.
• Naked Pairs / Triples: If two (or three) cells in a row, column, or box can only have the same two (or three) numbers, remove those numbers from the other cells in that row, column, or box.
• Hidden Pairs / Triples: Find numbers that show up in only two or three cells in a row, column, or box, even if there are other possible numbers too.
• Guess and Backtrack: For very challenging puzzles, guess a number and follow through to see if it leads to a valid solution. If not, backtrack and try another possibility.
• Use pencil and paper: Use pencil marks to keep track of possible numbers in each cell