Sudoku for Beginners: A Step-by-Step First Puzzle
A beginner solves a first Sudoku puzzle by repeatedly scanning the grid to find cells with only one possible digit, a technique called finding singles. This step-by-step guide walks you through your first puzzle from start to finish, using only simple scanning logic and minimal pencil marks. You will learn the fundamental process of elimination that makes Sudoku work, building confidence as you see the grid fill up. We will use a real example puzzle, explaining each move in plain terms and showing why it is correct based on the [Sudoku rules for beginners](/blog/sudoku-rules-for-beginners).
Your First Puzzle: The Starting Grid
Let's begin with a classic 'Easy' difficulty puzzle. The grid has nine 3x3 boxes, rows labeled 1-9, and columns labeled A-I. Your goal is to place the numbers 1 through 9 in every row, column, and box without repeating any. The given numbers are your clues. Our first action is not to guess, but to scan systematically.
Step 1: The Initial Scan for Obvious Singles
Start by looking at each 3x3 box. Find a box that already has several numbers filled in. For example, look at the center box. Which numbers are missing? Now, look at the empty cells in that box. For each empty cell, check its entire row and column. If you find a cell where, because of the numbers already in its row, column, and box, only one digit is possible, you have found a Naked Single. Place that number immediately. This is the core of the Sudoku scanning technique.
- Scan boxes first, as they contain the fewest cells.
- Work one number at a time. Ask, 'Where can 5 go in this box?'
Step 2: Re-Scan After Every Placement
Every time you place a new number, the puzzle changes. A new number blocks that digit in its row, column, and box, potentially creating new singles elsewhere. After placing your first number, stop and scan the entire grid again. Look at the boxes, rows, and columns affected by your new placement. Often, this reveals another Naked Single. This cycle of 'place a number, then re-scan' is the main engine for solving beginner puzzles.
Step 3: Using Pencil Marks for Hidden Singles
Soon, you will scan and find no obvious Naked Singles. This is when to use light pencil marks. Choose an empty cell and, by checking its row, column, and box, write small all the digits that could possibly go there. Do this for a few key cells in a crowded box or row. Now, look within a single house (a row, column, or box). If you see that a specific digit, like 7, can only go in one cell within that house, you have found a Hidden Single. Even though the cell has other pencil marks, 7 is its only possible placement for that particular house. Erase the pencil marks and write 7 in pen.
- Only pencil mark a small area (like one box) at a time to avoid clutter.
- Finding a Hidden Single often requires looking at just one row, column, or box in isolation.
Step 4: Recognizing Simple Patterns like Pairs
As more cells fill, you might see two empty cells in the same row, column, or box that share the exact same two pencil marks, like {3,8}. This is a Naked Pair. The powerful logic is this: those two digits must go in those two cells, in some order. Therefore, you can eliminate 3 and 8 as candidates from all other cells in that same row, column, or box. This elimination might create a new single for you to place. Recognizing pairs helps you clean up pencil marks and progress.
Step 5: Repeating the Cycle to Completion
The rest of the puzzle is a repetition of this cycle: 1) Scan for Naked Singles. 2) If stuck, add minimal pencil marks in a promising area. 3) Scan the pencil marks for Hidden Singles or simple patterns like Pairs. 4) Place a number, then immediately re-scan the whole grid. Each placed number gives you more information. Slowly and logically, the grid will fill up. The final numbers often fall into place quickly as the options become extremely limited.
Step 6: The Final Check
Once the last cell is filled, do a final verification. Check each row: does it contain 1-9 with no repeats? Check each column and each 3x3 box. If every house is complete, congratulations. You have solved your first Sudoku purely through logical deduction.
Key Facts
- ▪A Naked Single is a cell where only one number can fit because all other digits 1-9 are already present in its row, column, or 3x3 box.
- ▪The foundational Sudoku strategy is scanning: looking systematically across rows, columns, and boxes to find where numbers can and cannot go.
- ▪You should re-scan the entire puzzle after placing every single number, as each new placement changes the possibilities for other cells.
- ▪Pencil marks are temporary notes of possible digits for a cell and should be used only when you cannot find an obvious single.
- ▪A Hidden Single is a digit that has only one possible cell within a specific row, column, or box, even if that cell has other candidates.
- ▪A Naked Pair is two cells in the same row, column, or box that share the same two possible digits, allowing you to eliminate those digits from other cells in that area.
- ▪Beginner Sudoku puzzles are designed to be solvable using only the techniques of finding Singles (Naked and Hidden) and simple patterns like Pairs.
- ▪The process of elimination is the core logic of Sudoku; you determine a number by proving all other options are impossible.
- ▪Solving your first puzzle builds the mental framework for all future Sudoku logic, making more advanced techniques easier to learn later.
Frequently Asked Questions
What is the very first thing I should do when looking at a Sudoku puzzle?
Scan each 3x3 box for missing numbers. Look for a cell where, due to numbers already in its row and column, only one digit is possible. This is a Naked Single. Place it and re-scan.
When should I start using pencil marks?
Use pencil marks only when you scan the grid and cannot find any obvious Naked Singles. They help you see Hidden Singles, where a digit has only one possible cell in a row, column, or box.
What is the difference between a Naked Single and a Hidden Single?
A Naked Single is obvious: the cell has only one candidate. A Hidden Single requires checking one house; a digit appears as a candidate in only one cell there, even if that cell has other options.
How do I know if my solution is correct?
Check each row, column, and 3x3 box. Each must contain all digits 1-9 with no repeats. If any house has a duplicate or a missing number, a mistake was made earlier in the logic.
What if I get completely stuck on my first puzzle?
Re-scan the entire grid slowly. You likely missed a Hidden Single. Double-check your pencil marks for accuracy. An incorrect pencil mark can block progress. If needed, use a fresh puzzle labeled 'Easy'.
Is it cheating to use the hint button on SudokuHint.com?
No. The hint engine explains the logic for the next move, teaching you the technique. It is a learning tool, especially useful when you are stuck and want to understand why.