Logic Puzzles — One Solution, No Guessing
Each row, column, and 3×3 box contains 1–9 exactly once. Fewer clues = harder.
✨ The Fun Behind This
Why It's Fun
Sudoku trains logical deduction. Each cell is constrained by row, column, and box.
How It Works
Puzzles are generated by solving a full grid, then removing cells. Clue count determines difficulty.
Key Insights
- ●Minimum 17 clues needed for a unique 9×9 solution.
- ●Expert puzzles (20–24 clues) require advanced techniques like X-Wing or Swordfish.
- ●The name Sudoku means "single number" in Japanese.
Difficulty Presets — Click to Generate
For educational and informational purposes only. Verify with a qualified professional.
🎲 Fun Facts
Minimum 17 clues for a unique 9×9 solution.
— Math
Sudoku means "single number" in Japanese.
— Etymology
6.67×10²¹ possible completed 9×9 grids exist.
— Combinatorics
📋 Key Takeaways
- • Fill the 9×9 grid so each row, column, and 3×3 box contains 1–9 exactly once
- • No guessing needed—pure logic and deduction for well-designed puzzles
- • Difficulty = number of clues: Easy 40+, Medium 30–39, Hard 25–29, Expert 20–24
- • Every valid Sudoku has exactly one solution
💡 Did You Know?
📖 How Sudoku Works
Sudoku is a logic-based number-placement puzzle. The objective is to fill a 9×9 grid so that each column, each row, and each of the nine 3×3 sub-grids (boxes) contains the digits 1–9 exactly once.
- Row rule: Each row must contain 1–9, no repeats
- Column rule: Each column must contain 1–9, no repeats
- Box rule: Each 3×3 box must contain 1–9, no repeats
🎯 Solving Strategies
Naked Singles
If a cell has only one possible value, fill it in. Scan for cells where all other digits are placed.
Hidden Singles
In a row, column, or box, if a digit can only go in one cell, that cell must contain it.
Elimination
Cross out impossible candidates based on what's in the same row, column, and box.
Box-Line Reduction
If a digit in a box can only appear in one row/column, eliminate it from that row/column elsewhere.
📊 Difficulty Levels
| Level | Clues | Description |
|---|---|---|
| Easy | 40+ | Many given numbers, straightforward logic |
| Medium | 30–39 | Balanced challenge, some deduction needed |
| Hard | 25–29 | Fewer clues, advanced techniques helpful |
| Expert | 20–24 | Minimal clues, requires deep logic |
❓ FAQ
What makes a Sudoku valid?
A valid Sudoku has exactly one solution. Our generator ensures each puzzle has a unique solution before presenting it.
Can I print the puzzle?
Use the Copy button to copy the grid, then paste into a spreadsheet or document for printing.
Why does generation take a moment?
We verify that each puzzle has a unique solution by testing removals. Harder puzzles require more computation.
What is the minimum number of clues?
The minimum for a unique solution is 17. Our Expert level uses 20–24 for solvability.
🔢 Generation Algorithm
We generate a complete valid grid via backtracking with randomized digit order, then remove cells based on difficulty (fewer clues = harder). Removed cells become empty; remaining cells are fixed clues.
📚 References
Summary
Generate solvable 9×9 Sudoku puzzles at Easy, Medium, Hard, and Expert levels. Play in-browser with timer, validation, and solution reveal. Use Copy to export for printing.
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