Welcome, Sudoku New Players!

When you come to this page, it is very likely that you are a novice in Sudoku and want to know how to start playing this game. Hopefully, the tips offered on this page can help you quickly master the basics of gameplay. If you already know the Sudoku rules, let's start learning how to play Sudoku.

Tips for Beginners

When playing Sudoku games, always keep the following in mind:

• Each row, each column, and each 3x3 block must contain all nine digits 1 to 9.
• No digit can be repeated in each row, each column, or each 3x3 block.
• Each digit from 1 to 9 must appear exactly nine times in the 9x9 Sudoku grid.

With these in mind, you may determine the correct position for a digit or the correct digit for an empty cell.

A classic 9x9 Sudoku grid has nine rows, nine columns, and nine 3x3 blocks. A Sudoku puzzle is pre-filled with some digits from 1 to 9. More pre-filled digits in the grid will give you more information to find a unique possible position for a digit in a 9-cell unit (a row, a column, or a 3x3 block) or a unique possible digit for an empty cell. So, the more pre-filled digits in the grid, the easier the puzzle is.

Now, let's introduce a very basic but very useful technique for solving a Sudoku puzzle. If you master this technique, you can solve most of the puzzles at a low difficulty level.

Step 1: Pick a digit. Any digit will work, as long as it appears less than nine times in the Sudoku grid. However, if you choose a digit that has appeared more frequently in the grid, this can increase the success rate of finding the remaining correct positions for this digit.

Step 2: Check each 3x3 block that does not contain this digit. If there is only one cell that can accommodate this digit, then that cell is the correct position for the digit in this block. Actually, you may also go through each row or each column, but for beginners, it is a little bit easier to observe the unique possible position for the digit in a 3x3 block.

Step 3: Repeat steps 1 and 2 for all other digits, or the same digit if needed.

Repeating steps 1 and 2 with different digits will eventually solve most of the easy puzzles. However, if you have a more difficult puzzle, this technique alone cannot complete the game. You will need some other advanced techniques to do the job. As a beginner, you should start playing with easy puzzles first. After you feel that you are not a novice anymore, you can learn more advanced techniques and challenge yourself with more difficult puzzles.

We will demonstrate this technique with an example below. So, you can learn it more intuitively.

Example: Puzzle EZ

The Sudoku puzzle in Figure 1 above is a puzzle for beginners. Almost half of the cells have pre-filled digits. We will use this to demonstrate how to use the basic technique to solve a Sudoku puzzle.

Step 1: Pick a digit. In this example, we will choose the digit 7 first. The reason to choose this digit is that it has appeared in the grid more frequently (six times) than others, so the success rate of finding the remaining correct positions for this digit may be higher.

A side note: Our Sudoku game interface displays in the bottom right corner of each digit button in the digit panel how many times the digit is still left to fill in the Sudoku grid. The smaller the number, the more times it has appeared in the grid, so you don't have to count it yourself. In this example, the digit 7 has appeared six times in the grid. It must appear nine times eventually. So we still need to fill 3 more times of this digit in the grid, and this number "3" is shown in the bottom right corner of the digit 7 button in the digit panel.

Step 2: Check each 3x3 block that does not contain this digit. If there is only one cell that can accommodate this digit, then that cell is the correct position for the digit in this block.

In this example, six 3x3 blocks (B2, B3, B4, B5, B7, and B9) have already contained the digit 7. We need to check the remaining three blocks (B1, B6, and B8) to see if we can determine a position in each of these blocks for the digit 7.

Block B1: (Check for digit 7)

In block B1 of this puzzle, three cells have been pre-filled with digits other than the digit 7. The remaining six cells (R1,C2), (R1,C3), (R2,C2), (R2,C3), (R3,C1), and (R3,C3) are empty. We are going to check how many of these empty cells can possibly accommodate the digit 7 (Figure 2a). If there is only one, then that cell must be 7.

• As shown in Figure 2b, the cell (R1,C6) in row R1 is 7. Since each row can only contain the digit 7 once, the cell (R1,C2) and the cell (R1,C3) in the same row cannot be 7. These two cells are eliminated as possible positions for the digit 7 in block B1. Next, we need to check the remaining four empty cells (R2,C2), (R2,C3), (R3,C1), and (R3,C3).
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Figure 2c: Another Two Cells (R3,C1) and (R3,C3) Excluded for Digit 7
• As shown in Figure 2c, the cell (R3,C9) in row R3 is 7. Since each row can only contain the digit 7 once, the cell (R3,C1) and the cell (R3,C3) in the same row cannot be 7, and these two cells are also eliminated as possible positions for the digit 7 in block B1. Now two empty cells (R2,C2) and (R2,C3) remain.
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Figure 2d: One More Cell (R2,C2) Excluded for Digit 7
• As shown in Figure 2d, the cell (R9,C2) in column C2 is 7. Since each column can only contain the digit 7 once, the cell (R2,C2) in the same column cannot be 7, and it is eliminated as a possible position for the digit 7. The only remaining empty cell is the cell (R2,C3).
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Figure 2e: Cell (R2,C3) - a Possible Position for Dight 7
• The cell (R2,C3) is located in row R2, column C3, and block B1. No digit 7 appears in the same row, in the same column, or in the same 3x3 block. So the cell (R2,C3) can be a possible position for the digit 7 (Figure 2e).

As we can see in Figure 2e, the only possible position for the digit 7 in block B1 is the cell (R2,C3). Since each 3x3 block must contain the digit 7 once, we can conclude that the cell (R2,C3), as the only possible position for the digit 7 in block B1, must be 7. The cell (R2,C3) will be filled with the digit 7, as shown in Figure 2f below.

Block B6: (Check for digit 7)

We just successfully found a cell for the digit 7 in block B1. Block B6 is another block that does not contain the digit 7 yet. Let's see if we can find a unique cell for the digit in this block.

In block B6 of this puzzle, four cells have been pre-filled with digits other than the digit 7. The remaining five cells (R4,C8), (R5,C7), (R5,C9), (R6,C8), and (R6,C9) are empty. We are going to check how many of these empty cells can be possible positions for the digit 7 (Figure 3a). If only one cell can accommodate the digit 7, then this cell must be 7.

• As shown in Figure 3b, the cell (R5,C1) in row R5 is 7. Since each row can only contain the digit 7 once, the cell (R5,C7) and the cell (R5,C9) in the same row cannot be 7. These two cells are eliminated as possible positions for the digit 7 in block B6. Next, we need to check the remaining three empty cells (R4,C8), (R6,C8), and (R6,C9).
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Figure 3c: Another Two Cells (R6,C8) and (R6,C9) Excluded for Digit 7
• As shown in Figure 3c, the cell (R6,C4) in row R6 is 7. Since each row can only contain the digit 7 once, the cell (R6,C8) and the cell (R6,C9) in the same row cannot be 7, and these two cells are also eliminated as possible positions for the digit 7 in block B6. Now the only remaining empty cell is the cell (R4,C7).
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Figure 3d: Cell (R4,C8) - a Possible Position for Dight 7
• The cell (R4,C8) is located in row R4, column C8, and block B6. No digit 7 appears in the same row, in the same column, or in the same 3x3 block. So the cell (R4,C8) can be a possible position for the digit 7 (Figure 3d).

As we can see in Figure 3d, the only possible position for the digit 7 in block B6 is the cell (R4,C8). Since each 3x3 block must contain the digit 7 once, we can conclude that the cell (R4,C8), as the only possible position for the digit 7 in block B1, must be 7. The cell (R4,C8) will be filled with the digit 7, as shown in Figure 3e below.

We just finished two blocks, B1 and B6, and successfully determined a cell for the digit 7 in each block. Now we are going to check the last block B8 that does not contain the digit 7 yet.

Block B8: (Check for digit 7)

Block B8 is the last block that has not contained the digit 7 yet. Let's see if we can find a unique cell for the digit in this block.

In block B8 of this puzzle, four cells have been pre-filled with digits other than the digit 7. The remaining five cells (R7,C4), (R7,C6), (R8,C5), (R8,C6), and (R9,C4) are empty. We are going to check how many of these empty cells can be possible positions for the digit 7 (Figure 4a). If only one cell can accommodate the digit 7, then this cell must be 7.

• As shown in Figure 4b, the cell (R7,C7) in row R5 is 7. Since each row can only contain the digit 7 once, the cell (R7,C4) and the cell (R7,C6) in the same row cannot be 7. These two cells are eliminated as possible positions for the digit 7 in block B8. Next, we need to check the remaining three empty cells (R8,C5), (R8,C6), and (R9,C4).
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Figure 4c: One More Cell (R9,C4) Excluded for Digit 7
• As shown in Figure 4c, the cell (R9,C2) in row R9 is 7. Since each row can only contain the digit 7 once, the cell (R9,C4) in the same row cannot be 7, and it is also eliminated as possible positions for the digit 7 in block B8. Now two empty cells (R8,C5) and (R8,C6) remain.
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Figure 4d: Another Cell (R8,C6) Excluded for Digit 7
• As shown in Figure 4d, the cell (R1,C6) in column C6 is 7. Since each column can only contain the digit 7 once, the cell (R8,C6) in the same column cannot be 7, and it is eliminated as a possible position for the digit 7. The only remaining empty cell in block B8 is the cell (R8,C5).
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Figure 4e: Cell (R8,C5) - a Possible Position for Dight 7
• The cell (R8,C5) is located in row R8, column C5, and block B8. No digit 7 appears in the same row, in the same column, or in the same 3x3 block. So the cell (R8,C5) can be a possible position for the digit 7 (Figure 4e).

As we can see in Figure 4e, the only possible position for the digit 7 in block B8 is the cell (R8,C5). Since each 3x3 block must contain the digit 7 once, we can conclude that the cell (R8,C5), as the only possible position for the digit 7 in block B8, must be 7. The cell (R8,C5) will be filled with the digit 7, as shown in Figure 4f below.

At this point, step 2 is done. We completed all three 3x3 blocks that did not originally contain the digit 7. Fortunately, we can find the unique possible cell position for the digit 7 in each block. In fact, sometimes we may also encounter the fact that it is impossible to determine in which cell the digit should be placed at the moment. It doesn't matter. Let's put it aside for now, move to the next block first, and then come back to try again later.

Step 3: Repeat steps 1 and 2 for all other digits, or the same digit if needed. In this example, the digit 1 is the pick for next. This pick can be arbitrary. But usually, we look for a digit that has been filled in more times in the Sudoku grid.

As shown in Figure 5, there are four 3x3 blocks (B1, B3, B4, and B8) that do not contain the digit 1 at the moment. We are going to see if we can find a unique possible cell for the digit 1 in each of these blocks.

Block B1: (Check for digit 1)

The digit 1 is not in block B1 yet. Four cells have been filled with digits other than the digit 1. The remaining five cells (R1,C2), (R1,C3), (R2,C2), (R3,C1), and (R3,C3) are empty. We are going to check how many of these empty cells can be possible positions for the digit 1 (Figure 6a). If only one cell can accommodate the digit 1, then this cell must be 1.

• The cell (R3,C5) in row R3 is 1. So, the cell (R3,C1) and the cell (R3,C3) in the same row cannot be 1, and they are eliminated as possible positions for the digit 1 in block B1.
• The cell (R1,C2) is located in row R1, column C2, and block B1. No digit 1 appears in the same row, in the same column, or in the same 3x3 block. So the cell (R1,C2) can be a possible position for the digit 1 in block B1.
• The cell (R1,C3) is located in row R1, column C3, and lock B1. No digit 1 appears in the same row, in the same column, or in the same 3x3 block. So the cell (R1,C3) can be a possible position for the digit 1 in block B1.
• The cell (R2,C2) is located in row R2, column C2, and block B1. No digit 1 appears in the same row, in the same column, or in the same 3x3 block. So the cell (R2,C2) can be a possible position for the digit 1 in block B1.

As shown in Figure 6b, three cells (R1,C2), (R1,C3), and (R2,C2) are still possible for the digit 1. So, we cannot determine which cell should be filled with the digit 1 yet. We may just leave it aside for now and come back later.

Block B3: (Check for digit 1)

The digit 1 is not in block B3 yet. Five cells have been filled with other digits. The remaining four cells (R1,C8), (R2,C9), (R3,C7), and (R3,C9) are empty. We are going to check how many of these empty cells can be possible positions for the digit 1 (Figure 7a). If only one cell can accommodate the digit 1, then this cell must be 1.

• The cell (R3,C5) in row R3 is 1. So, the cell (R3,C7) and the cell (R3,C8) in the same row cannot be 1, and they are eliminated as possible positions for the digit 1 in block B3.
• The cell (R8,C8) in column C8 is 1. So, the cell (R1,C8) in the same column cannot be 1, and it is eliminated as a possible position for the digit 1 in block B3.
• The cell (R2,C9) is located in row R2, column C9, and block B3. No digit 1 appears in the same row, in the same column, or in the same 3x3 block. So the cell (R2,C9) can be a possible position for the digit 1 in block B3.

As we can see in Figure 7b, the only possible position for the digit 1 in block B3 is the cell (R2,C9). Since each 3x3 block must contain the digit 1 once, we can conclude that the cell (R2,C9), as the only possible position for the digit 1 in block B3, must be 1. The cell (R2,C9) will be filled with the digit 1, as shown in Figure 7c below.

We just successfully found a unique cell for the digit 1 in block B3. Let's go check the next block that does not contain the digit 1 yet.

Block B4: (Check for digit 1)

The digit 1 is not in block B4 yet. Four cells have been filled with digits other than the digit 1. The remaining five cells (R4,C1), (R4,C3), (R5,C3), (R6,C1), and (R6,C2) are empty. We are going to check how many of these empty cells can be possible positions for the digit 1 (Figure 8a). If only one cell can accommodate the digit 1, then this cell must be 1.

• The cell (R4,C7) in row R4 is 1. So, the cell (R4,C1) and the cell (R4,C3) in the same row cannot be 1, and they are eliminated as possible positions for the digit 1 in block B4.
• The cell (R5,C6) in row R5 is 1. So, the cell (R5,C3) in the same row cannot be 1, and it is eliminated as a possible position for the digit 1 in block B4.
• The cell (R9,C1) in column C1 is 1. So, the cell (R6,C1) in the same column cannot be 1, and it is eliminated as a possible position for the digit 1 in block B4.
• The cell (R6,C2) is located in row R6, column C2, and block B4. No digit 1 appears in the same row, in the same column, or in the same 3x3 block. So the cell (R6,C2) can be a possible position for the digit 1 in block B4.

As we can see in Figure 8b, the only possible position for the digit 1 in block B4 is the cell (R6,C2). Since each 3x3 block must contain the digit 1 once, we can conclude that the cell (R6,C2), as the only possible position for the digit 1 in block B4, must be 1. The cell (R6,C2) will be filled with the digit 1, as shown in Figure 8c below.

Again, we successfully found a unique cell for the digit 1 in block B4. We will move to the next block that does not contain the digit 1 yet.

Block B8: (Check for digit 1)

The digit 1 is not in block B8 yet. Five cells have been filled with digits other than the digit 1. The remaining four cells (R7,C4), (R7,C6), (R8,C6), and (R9,C4) are empty. We are going to check how many of these empty cells can be possible positions for the digit 1 (Figure 9a). If only one cell can accommodate the digit 1, then this cell must be 1.

• The cell (R5,C6) in column C6 is 1. So, the cell (R7,C6) and the cell (R8,C6) in the same column cannot be 1, and they are eliminated as possible positions for the digit 1 in block B8.
• The cell (R9,C1) in row R9 is 1. So, the cell (R9,C4) in the same row cannot be 1, and it is eliminated as a possible position for the digit 1 in block B8.
• The cell (R7,C4) is located in row R7, column C4, and block B8. No digit 1 appears in the same row, in the same column, or in the same 3x3 block. So the cell (R7,C4) can be a possible position for the digit 1 in block B8.

As we can see in Figure 9b, the only possible position for the digit 1 in block B8 is the cell (R7,C4). Since each 3x3 block must contain the digit 1 once, we can conclude that the cell (R7,C4), as the only possible position for the digit 1 in block B8, must be 1. The cell (R7,C4) will be filled with the digit 1, as shown in Figure 9c below.

We have completed all four 3x3 blocks that did not originally contain the digit 1 and found the unique possible position for the digit 1 in three of them. Now we can repeat the process of steps 1 and 2 with the digit 1 again or with another digit. Either one is okay. We are not going into detail for the rest of this solving process. Just repeat steps 1 and 2 with all digits (for several times if needed), and this puzzle will be solved. The solution for this puzzle is shown below in Figure 10.

The technique introduced here is called hidden single. The idea behind this technique is that since each 3x3 block must contain each digit once, if we can find only one cell that can possibly accommodate a certain digit in a 3x3 block, then that cell must be filled with that digit. In fact, this technique can also be applied to a row or a column. You can learn more about this technique at the "Hidden Single" page.

At this point, you may go play some very easy Sudoku games (Kindergaten: Very Easy Sudoku Puzzles). With the technique you just learned here, you should be able to solve all the puzzles at that level. After you feel more comfortable with this technique, you can upgrade to play Sudoku puzzles that are still easy but have fewer pre-filled digits (Elementary: Easy Sudoku Puzzles). You should be able to solve these puzzles as well.

Later, when you feel those puzzles at the two lowest difficulty levels are too easy, you may want to challenge yourself with more difficult Sudoku puzzles. Then you will need to master more advanced techniques to solve the puzzles. We provide a set of tutorials, Sudoku Solving Techniques, for you. After learning those advanced techniques, you should be able to solve more difficult puzzles at a higher difficulty level.