Sudoku Basics: Recognizing Patterns

Sudoku puzzles are built on logic and careful analysis. While some Sudoku players can sometimes solve even medium Sudoku puzzles through luck, learning the game to its core can provide more consistent results. Some prefer playing on their phones by tapping their preferred app icon for Sudoku, while others like playing on a computer on free-to-play websites like

Regardless, for many beginners, understanding the basic rules, terms and techniques can give way to a more enjoyable Sudoku experience, and is key to reaching Sudoku mastery.

Recognizing patterns within the game is a basic skill that every Sudoku player should learn and try out in easy Sudoku puzzles, and is necessary in learning advanced pattern-based techniques. Today, we’ll be learning how to identify a basic pattern called a “complete segment”, how you can use this pattern to your advantage in-game and even more Sudoku tips!

Importance of Recognizing Patterns in Free Sudoku Puzzles

Every game of Sudoku can be solved through pure logic, and knowing even the simplest patterns can help slice up the grid to become a lot easier to fill in with digits. Recognizing patterns in a Sudoku game makes full use of other basic skills like scanning and seeing intersections, and with the right techniques, can significantly improve your speed and your solving tactics.

To be able to tackle harder difficulty Sudoku puzzles, it's best to take notes of basic skills like these. Keep these tips in mind while playing and you'll be able to explore more of the Sudoku world and have even more fun!

Pattern: Complete Segment

Let’s begin learning one of the most basic patterns to recognize in Sudoku—the complete segment. A complete segment is either a row or column of three cells in the same box that are filled in with givens or answered numbers. For example, cells r1c5,r2c5 and r3c5 all have numbers, is this a complete segment? Yes, it is!

How about if the cells in a single row, like r2c2, r2c3 and r2c4, are filled in? Is this a complete segment? No, it is not. A complete segment must be in one box, and the numbers should be three adjacent cells horizontally or vertically.

To make it easier to recognize in-game, let’s use this sample Sudoku grid:

As you can see, there are three numbers in box 5, and they all occupy the same row, in row 5. This is a complete segment that we can use to solve other nearby boxes. Note the other numbers in boxes 4 and 6, as they will be integral to our usage of this pattern.

How Does It Work?

Now, let’s use the complete segment above to fill in a cell. How do you know where your target cell is? The cell you’re going to fill in is in the same row or column as the complete segment, and it’s best to choose a box with more givens. And in this case, we’re gonna fill in a cell within row 5, box 6.

The first thing you need to do is to look for one digit that doesn’t appear in the box, row and/or column where the complete segment is. Keep in mind that the number you’ll use to fill in a cell must not appear in the same row, column or box as the complete segment.

The segment we’ll be using has the numbers 1, 9 and 8 in box 5, row 5. In the same row, there are numbers 2 and 5. Either of these numbers can’t be used as they are in the same row. So by that logic, we can use the digit 6 in box 4. Now that we’ve determined the number we’re going to use to fill in a cell, let’s solve for its proper placement using the complete segment pattern.

Solving Using Complete Segment

Since there’s already a 6 in box 4, we only have to solve for boxes 5 and 6. So in both these boxes, the 6 cannot go anywhere in row 4 as there’s already a 6 in box 4, r4c1. As for row 5, we can’t put it in box 5 since that’s where the complete segment is. But we can pencil mark a 6 in r5c8.

For row 6, we can’t determine which cells it can go to in box 5, so we pencil mark 6 into all three of them. And since we’ve pencil marked that whole row, we no longer need to pencil mark for box 6.

With this, we can then confirm that the 6 for box 6 is in cell r5c8.

Congratulations! You’ve just filled in a cell by recognizing a pattern!

Another Example

When it comes to Sudoku, to play better is to practice constantly. Let’s fill in another cell using a different example, like in this sample Sudoku grid:

Now, just like we did in the previous Sudoku example, we look for a pattern and identify it. Here, we have a complete segment in box 7. We have the numbers 2, 8 and 4 in a vertical complete segment, and our target cell is within column 3 of box 4.

Now we look for a number to use for filling in. Remember, it can’t be a number that appears in the same box, row and column of the complete segment. By eliminating possible digits to use using those conditions, we can only use the number 1 in cell r3c2.

Using scanning and intersections, we determine that the whole column 2 in box 4 can’t be filled in with the number 1. We also pencil mark the blanks in column 1, box 7 with 1 as this box has more givens, which also eliminates the whole column 1 of box 4 as possible cells to put it in. As a result, we can safely put 1 in r5c3.

Well done! You’ve filled in another cell by recognizing and using a pattern in your solving process! If you want to become more confident in using it, you can always practice on easy Sudoku puzzles first.