How to Solve a Very Difficult Sudoku Puzzle

Solving the most challenging sudoku puzzles is a difficult but rewarding pursuit

Sudoku puzzles are difficult Japanese number puzzles akin to a numerical crossword puzzle using only the numbers one through nine. The grid is a nine by nine grid (81 total squares) and the goal is to fill each row, column, and three-by-three sub-squares with the numbers one through nine. These puzzles range in difficulty, with some of them requiring hours of focused concentration to solve. Having a variety of sudoku strategies at your disposal allows you to recognize patterns and solve the most difficult sudoku puzzles.

Instructions

1. Look for any easy numbers that you can immediately fill in. Go through the puzzle number-by-number looking for any empty boxes that must be fill with a particular digit. The goal at the beginning of solving a difficult sudoku puzzle is to fill in as many boxes as possible, which will help you figure out where the other numbers go as you progress through the puzzle.

2. Look for rows and columns that have the most numbers filled in once you have gone through each number individually. Start with rows that already have six or more numbers filled in, and then move down to row with five or four numbers (rows with only three are usually too difficult to solve immediately). For example, a row with seven numbers filled in offers the possibility that you can easily complete it by using the process of elimination. Look for intersecting rows that cancel the possibility of being able to put certain numbers in a cell until you have the right one.

3. Look at each box of nine and determine which numbers are missing. Compare these missing numbers to those that have already been placed in the rows and columns that intersect the box of nine. This will usually yield at least a couple of quick solutions. Make sure you start with the boxes of nine with the most numbers already filled in to increase you chances of finding more solutions.

Tips & Warnings

• Use a pencil and keep track of which numbers you have already exhausted while completing the puzzle.

• Avoid the urge to look for a solution to a very difficult puzzle, even if you think filling in a single cell will provide a breakthrough. The most mentally taxing puzzles are the most rewarding to finish. Cheating by filling in cells according to the solution will rob you of the pleasure that completing a particularly nasty puzzle brings.

References

• SearchWarp: Secret Sudoky Tips and Techniques
• Said What: Sudoku Puzzle Strategies