8x8 Hard Sudoku Puzzles

About Sudoku Puzzles

Sudoku is a logic-based, popular number-placement puzzle. The Sudoku grid is divided into sub-grids called "boxes" or "regions." The goal is to fill the grid with digits from 1 to grid-size 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 8x8 grid size made up of eight 4x2 sub-grids.
• Unique Numbers: Each row, column, and sub-grid must contain all digits from 1 to 8 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