Sudoku is played on a 9x9 grid, divided into nine smaller 3x3 boxes. The goal is simple: fill each row, column, and box with the numbers 1 to 9 — without repeating any number within the same line or square. Most puzzles start with a few numbers already placed to get you going. From there, it's up to your logic and patience to complete the grid.
Scan the puzzle for rows, columns, or boxes that already have many numbers filled in — these are the easiest places to make progress. Use the process of elimination to figure out what numbers can or can’t go in certain spots. Pencil marks (small notes of possible values) are your best friend for tougher puzzles. Remember: if you’re guessing, you’re probably overlooking a logical move.
When the easy placements dry up, try these more advanced tactics:
1. Look for hidden singles. Sometimes, a number might not be the only candidate in a cell, but it may be the only candidate in a row, column, or box. These are called hidden singles. Scanning for them is often more fruitful than scanning for obvious numbers.
2. Try cross-hatching. Pick a number, say 5, and scan through each 3x3 box to eliminate where it can’t go, based on where 5s already exist in rows and columns. This visual technique helps isolate the right spot for that number.
3. Use box-line reduction. If a number in a 3x3 box can only appear in one row (or column), you can eliminate that number from the same row (or column) outside of the box. This tactic often goes unnoticed by casual players and is great for tightening down possibilities.
4. Spot X-Wings. This is a powerful intermediate technique. If a candidate number appears only in two possible cells in two different rows (and those cells align in the same columns), you’ve found an “X-Wing.” This allows you to eliminate that candidate from other cells in those two columns. It sounds complex, but mastering this can help break through tougher puzzles.