What Is Sudoku?
Sudoku is a number-placement puzzle played on a 9×9 grid divided into nine 3×3 boxes. The goal is simple: fill every row, column, and box with the digits 1 through 9 — each digit appearing exactly once. No math required; it's purely logic.
Understanding the Rules
- Every row must contain the digits 1–9 with no repeats.
- Every column must contain the digits 1–9 with no repeats.
- Every 3×3 box must contain the digits 1–9 with no repeats.
The puzzle starts with some numbers already placed — called givens or clues. Your job is to deduce the rest.
Step 1: Scan for Single Candidates
Start by scanning each empty cell and asking: what numbers are already in this row, column, and box? If only one digit is missing, that's your answer. This technique — called naked singles — solves a surprising portion of beginner puzzles on its own.
Step 2: Use the Elimination Method
For each number from 1 to 9, look at where it can still legally go within a box. If it can only fit in one cell, place it there. Work box by box, row by row. This approach is called cross-hatching and is the most intuitive technique for new solvers.
Step 3: Look for Hidden Singles
Sometimes a digit can go in multiple cells within a unit (row, column, or box) — but only one of those cells is valid once you consider all three constraints together. Scan carefully: a number that appears to have two candidates in a box might be forced into one cell when you check its row and column.
Step 4: Pencil in Candidates
When you get stuck, write small candidate numbers in empty cells. This visual map reveals patterns and helps you apply more advanced techniques without losing track. Most physical Sudoku books leave space for this; digital apps often include a "notes" feature.
Common Beginner Mistakes to Avoid
- Guessing too early — Sudoku has a unique solution. If you're guessing, you've likely missed a logical step.
- Ignoring one constraint — Always check row, column, AND box before placing a number.
- Skipping the pencil marks — Once you hit intermediate difficulty, tracking candidates manually becomes essential.
Difficulty Levels Explained
| Level | Techniques Needed | Clues Given (approx.) |
|---|---|---|
| Easy | Naked singles, cross-hatching | 36–40 |
| Medium | Hidden singles, candidate lists | 30–35 |
| Hard | Naked/hidden pairs, pointing pairs | 24–29 |
| Expert | X-Wings, Swordfish, chains | 17–23 |
Ready to Practice?
The best way to improve is consistent practice. Start with easy puzzles and resist the urge to jump to hard ones too quickly. Each level introduces new logical patterns, and building a strong foundation makes harder puzzles far more enjoyable. Grab a beginner book or open a reputable Sudoku app and work through a puzzle a day — you'll be surprised how fast your speed and confidence grow.