Master these techniques and you can solve any sudoku puzzle
Naked Single
Beginner
A cell where only one number is possible — all other digits are already used in its row, column, or box.
5
3
7
6
1
9
5
9
8
6
8
6
3
4
8
3
1
7
2
6
6
2
8
4
1
9
5
8
7
9
Target cell Key clues Eliminated
How to spot it
1Pick any empty cell and look at its row, column, and 3×3 box.
2List every number that already appears in those three groups.
3If only one number (1–9) is missing from all three groups, that's the answer.
Example: Row has 5,3 · Column has 6,9,8,4,7 · Box has 5,3,6,9,8 → only 4 is missing. The answer is 4.
Hidden Single
Beginner
A number that can only fit in one cell within a row, column, or box — even if that cell has multiple candidates.
2
6
7
1
6
8
7
9
1
9
4
5
8
2
1
4
4
6
2
9
5
3
2
8
9
3
7
4
4
5
3
6
7
3
1
8
Target cell Key clues Eliminated
How to spot it
1Pick a number (1–9) and focus on one row, column, or box.
2Find every empty cell in that group where the number could go.
3If only one empty cell can hold that number, place it there.
Example: Look at column 6 and ask: "Where can 9 go?" Many cells are blocked by existing 9s in their rows or boxes. Only one cell remains open for 9.
Pointing Pair
Intermediate
When a number's only possible cells in a box all fall in the same row or column, that number can be removed from the rest of that row or column.
3
2
6
9
3
1
1
8
4
8
1
2
9
7
8
6
7
8
2
2
9
1
3
5
5
3
4
Target cell Key clues Eliminated
How to spot it
1Look at a 3×3 box and pick a number.
2Find all the empty cells in the box where that number could go.
3If those cells all share a row (or column), the number must go in the box — so cross it out everywhere else in that row (or column).
4This often reveals a Naked Single or Hidden Single elsewhere.
Example: In the top-middle box, a number can only appear in row 2. That locks it to the box — so eliminate it from all other cells in row 2 outside the box.
Naked Pair
Intermediate
Two cells in the same row, column, or box that each have exactly the same two candidates. Those two numbers must go in those two cells, so they can be removed from all other cells in that group.
1
2
3
4
5
6
Target cell Key clues Eliminated
How to spot it
1Find two empty cells in the same row, column, or box.
2Check if both cells have exactly the same two candidates (e.g. both only allow {3, 7}).
3Even though you don't know which cell gets 3 and which gets 7, you know both numbers are "used up" in those two cells.
4Remove 3 and 7 as candidates from every other cell in that row, column, or box.
5Look for any cell that now has only one candidate left.
Example: If two cells in a column both show only {7, 8}, those two numbers are reserved for those cells. Any other cell in the column that listed 7 or 8 as a possibility can have them crossed off.