Most beginners approach a fresh Sudoku grid the same way: eyes darting around the puzzle, looking for any number that might reveal itself. It feels intuitive — scan everything, grab what you can, fill as you go. But this random approach leaves a lot of logical value on the table. The most efficient place to start a Sudoku puzzle isn't wherever you happen to look first. It's the corners.
Why the Corners Give Up Information Faster
Every Sudoku grid is divided into nine 3×3 boxes. The corner boxes — top-left, top-right, bottom-left, bottom-right — are each constrained by exactly two adjacent boxes sharing their row and column groups. The center box is constrained by four. But here's the key insight: corner and edge boxes share their rows and columns with fewer competing regions, which means the digits that flow into them from neighboring boxes tend to be more decisive.
When you examine a corner box, you're working with a tight intersection of row constraints, column constraints, and box constraints all converging on just nine cells. Fewer cells means fewer candidates per digit, and fewer candidates means faster forced placements. A digit that has five possible positions in the center box might have only two in a corner box — and two possible positions is almost always solvable with one more cross-reference.
The Practical Technique: Box Scanning From Corners Out
Here's a method that experienced solvers use automatically. Start with the top-left corner box. For each digit 1 through 9, count how many times it already appears in the rows and columns that pass through that box. If a digit already appears in two of the three rows crossing that box, it can only go in the remaining row — and within that row, it can only go in whichever cells aren't blocked by column constraints. Often, this narrows it to a single cell.
Once you've extracted everything the top-left corner offers, move to an adjacent corner — say, top-right. You'll find that the digits you just placed in the top-left have rippled new constraints into the top-right box, making it even more productive. Work your way around the four corners before touching the middle boxes, and you'll typically have 10 to 15 digits placed before you ever deal with the more complex center regions.
What About Easy Puzzles?
On an easy Sudoku, this approach might feel like overkill — there are enough given digits scattered everywhere that you can fill cells almost anywhere. But the corner-first habit pays enormous dividends when you graduate to medium and hard puzzles. Hard Sudoku grids often have very few given digits in the center boxes precisely because setters know those regions are harder to constrain. The corners, even in hard puzzles, tend to have slightly more starter digits or benefit more from cross-box logic.
Building the corner-first habit on easy puzzles means it becomes automatic before you need it on harder ones. You won't have to think about where to start — your eye will go directly to the most productive region by instinct.
One More Reason: Psychological Momentum
There's a non-technical benefit too. Starting in a corner and quickly placing two or three digits builds solving momentum. You see progress immediately, your confidence goes up, and you enter the harder sections of the grid with a working framework of placed digits rather than staring at a mostly empty page. Puzzle solving is partly logical and partly psychological — and corner-first gives you both a logical and an emotional head start.
Next time you pick up a Sudoku, resist the urge to scan randomly. Go straight to the top-left corner. Work the box. Then move to the next one. You'll be surprised how quickly the rest of the grid starts to open up.