Sudoku Solving Techniques: From Naked Singles to Pointing Pairs and X-Wing

By the Happy Life Games team · Updated October 19, 2026 · 6 min read

A good Sudoku never needs a guess. Every digit can be worked out from what's already on the grid. What separates an easy puzzle from a fiendish one is which techniques you need to find the next digit.

This guide climbs that ladder, with a small example for each step. Rows are numbered 1 to 9 from top to bottom and columns 1 to 9 from left to right, so "R2C7" means row 2, column 7.

A quick word on the rules and the history

Fill the grid so that every row, every column and every box contains each digit exactly once. On a standard board that means 1 to 9 in nine rows, nine columns and nine 3×3 boxes. The modern puzzle first appeared in 1979 in an American Dell puzzle magazine under the name "Number Place." The Japanese publisher Nikoli later popularized it under the name Sudoku, and it became a worldwide newspaper fixture in the mid-2000s.

Our Sudoku Easy eases you in with 4×4 and 6×6 boards before moving to the full 9×9. From level 11 you get three hearts, and a wrong number costs one. That's a gentle push to solve by logic instead of trial and error.

Step 1: Full house (the last empty cell)

If a row, column or box has eight digits filled in, the ninth cell gets the one missing digit. Scanning for nearly complete units is the fastest way to start.

Step 2: Hidden singles (only one spot for a digit)

Pick a digit and a box, and ask "where in this box can the 4 go?" This is often called cross-hatching. Suppose the top-left box (rows 1–3, columns 1–3) has no 4 yet. There's a 4 in row 1 further right and another 4 in row 3. Those rule out every empty cell of the box in rows 1 and 3. If column 1 also contains a 4 lower down, then R2C1 is ruled out too. If R2C2 is already filled, the only spot left is R2C3. That cell must be a 4, even if other digits could also fit there.

The same question works for a row or column. "Where can the 7 go in row 5?" is called a hidden single in a line.

Step 3: Naked singles (only one digit for a cell)

Now flip the question. Pick an empty cell and list what can't go there. Say R5C5 sees 1, 2 and 3 in its row, 4, 6 and 8 in its column, and 5 and 9 in its box. That's eight different digits, so the only candidate left is 7.

In Sudoku Easy the hint button explains itself in the same terms. It might say a cell is the last empty one in its row, that a digit has only one spot in a box, or that only one digit fits once you check the row, column and box together. Most easy and medium puzzles can be solved with nothing more.

Step 4: Pencil marks

Beyond singles, you need candidates. These are the small digits you jot in a cell's corner to show what it could still be. On paper, fill them in for every empty cell after you've placed all the easy singles, and update them each time you place a digit. The techniques below all work by removing candidates until a single appears.

Step 5: Naked pairs

Suppose two cells in row 3, R3C2 and R3C6, both have exactly the candidates {2, 7}. One of them will be 2 and the other 7. You don't know which yet, but together they use up both digits. So no other cell in row 3 can be 2 or 7, and you can erase those candidates from the rest of the row. If the two cells also share a box, erase 2 and 7 from the rest of that box as well.

Step 6: Pointing pairs

This is where Sudoku starts to feel clever. Look at the top-left box and the digit 5. Suppose the only cells in that box that can still hold a 5 are R2C1 and R2C3, so both are in row 2. The box needs a 5 somewhere, so the 5 for that box is definitely in row 2. That means row 2's 5 is used up inside this box, and no cell in row 2 outside the box can be 5. Erase 5 from R2C4 through R2C9.

The pair "points" along its row (or column) and clears it. It works the same with three cells in a line, called a pointing triple. In Sudoku Easy, this is the technique behind the "Pairs point the way" levels.

The mirror image: box-line reduction

Reverse the logic. If in row 8 the digit 3 can only go in cells that all sit inside one box, say R8C7 and R8C9, then that box's 3 must be in row 8. Erase 3 from every other cell of that box that isn't in row 8. This is sometimes called "claiming." Together, pointing and claiming are known as locked candidates.

Step 7: The X-Wing

The X-Wing is the first "pattern" technique most solvers learn, and it's easier than its reputation. Look at one digit across two rows. Suppose that in row 2 the digit 6 can only go in columns 3 and 8, and in row 7 it can also only go in columns 3 and 8:

Row 2 needs a 6, so it goes in C3 or C8. Row 7 also needs a 6, in C3 or C8, but not in the same column as row 2's, because a column can't hold two 6s. So there are only two ways it can play out: R2C3 and R7C8, or R2C8 and R7C3. Either way, columns 3 and 8 each get their 6 from rows 2 and 7. That means you can erase 6 from every other cell in columns 3 and 8.

The four corners form a rectangle, and the two possible answers make an X across it, which is where the name comes from. It also works with rows and columns swapped.

A sensible order of attack

1. Sweep for full houses and hidden singles digit by digit, 1 through 9. This finds the most digits for the least effort.
2. Check crowded cells for naked singles.
3. When nothing obvious is left, write pencil marks for the whole grid.
4. Look for naked pairs, then pointing pairs and box-line reductions.
5. Only then hunt for X-Wings, one digit at a time.
6. After any elimination, go back to step 1. A single erased candidate often creates a new single somewhere else.

Common mistakes

• Guessing when stuck. A guess that happens to work teaches you nothing, and in Sudoku Easy a wrong guess costs a heart. If you're stuck, there's a technique you haven't spotted yet.
• Forgetting to update candidates. Stale pencil marks lead to false pairs and wrong eliminations. Update every time you place a digit.

Frequently asked questions

Do I need X-Wing for Sudoku Easy?

No. Our game is graded with singles and pointing pairs, so every puzzle can be solved without advanced patterns. X-Wing is worth learning for harder newspaper and book puzzles.

How does the hint work in Sudoku Easy?

It highlights a cell you can fill next, along with the row, column or box that proves it, and gives the reason in a short message, for example that the digit has only one spot in that box. It teaches the technique as well as the answer.