Techniques › Pointing
Pointing
A digit confined to one line inside a box clears that digit from the rest of the line.
Look at one box and one digit. If every cell where that digit could still go lies in the same row, then the digit must be somewhere in that row — you do not know where, but you know it is inside the box. So it cannot be anywhere else along that row, outside the box.
Pointing is the first technique that eliminates candidates rather than placing a digit, and that shift is the real step up in sudoku. You are no longer asking "what goes here?" but "what can I rule out?" Most puzzles above easy need at least one.
A worked example
Taken from a real puzzle in our bank, at the point where this was the cheapest move available. Pattern candidates are marked in amber; anything the step eliminates is struck through in red.
| 9 | 2 | 4 | 18 | 7 | 6 | 3 | 5 | 18 |
| 8 | 1 | 7 | 3 | 5 | 9 | 6 | 2 | 4 |
| 3 | 6 | 5 | 4 | 2 | 18 | 78 | 17 | 9 |
| 2 | 5 | 1 | 6 | 8 | 3 | 4 | 9 | 7 |
| 7 | 4 | 3 | 9 | 1 | 2 | 5 | 8 | 6 |
| 6 | 8 | 9 | 7 | 4 | 5 | 1 | 3 | 2 |
| 5 | 9 | 2 | 18 | 6 | 178 | 78 | 4 | 3 |
| 1 | 7 | 8 | 2 | 3 | 4 | 9 | 6 | 5 |
| 4 | 3 | 6 | 5 | 9 | 178 | 2 | 17 | 18 |
- NudgeDigit 1 is pinned to one line inside a box, which rules it out further along that line.
- WherePointing in box 9, row 9: r9c8, r9c9
- Do itRemove r9c6 ≠ 1
How to spot it
For each box, take each unplaced digit and see whether its remaining cells share a row or a column. Two or three cells in a line is the pattern.
Where you will meet it
Pointing sits at tier 1 of our ladder, which means it first becomes necessary at Easy. Puzzles below that band never require it, though it may still appear as a shortcut.
Read next
- Claiming A digit confined to one box inside a line clears that digit from the rest of the box.
- Hidden Single A digit with only one home left in a house, even though that cell has other candidates.
- Naked Pair Two cells in a house holding the same two candidates lock those digits away from the rest.