Lesson 06 of 08 — Advanced
Naked triple technique
A naked triple is three cells in one unit whose candidates, taken together, come to exactly three digits. The three digits must fill those three cells between them, so none of them can appear anywhere else in the unit.
What it does
The three cells do not each need all three digits. {1, 2}, {2, 3} and {1, 3} is a triple, and so is {1, 2, 3} beside {1, 2} and {1, 3}. What matters is the total: three digits, three cells.
Because the digits are confined to those cells, the triple removes three digits from a whole row, column or box at once, which is why it so often breaks a puzzle open.
A worked example
Find three cells with three digits between them
Scan a unit for a group of three cells whose candidates together add up to exactly three digits. Two-mark cells are the easiest starting point.
Check nothing spills over
Every candidate in all three cells has to sit inside the same three digits. A fourth digit anywhere in the group makes it a larger set, not a triple, and the eliminations do not apply.
Remove the three digits from the unit
Delete all three digits from every other cell of the row, the column or the box.
Look for the pair hiding inside
A triple with one three-mark cell and two two-mark cells usually leaves singles behind. Place everything that becomes certain before searching for the next pattern.
How to spot it
- Units with several cells holding two or three candidates. The more of them there are, the more likely three of them share the same three digits.
- A cell showing three candidates is worth a second look: it may be the anchor of a triple with two two-mark cells beside it.
- Triples are rarer than pairs, so exhaust pairs and locked candidates first and treat a triple as the answer to a puzzle that has otherwise stalled.
All three cells must share one unit, and their candidates must not reach beyond the same three digits. A cell with a fourth candidate breaks the group, and applying the eliminations anyway can remove the digit the puzzle actually needed. If a unit gives you a group that looks like a triple but one cell has an extra mark, you have found a larger set, not a triple.
Practise it in Sudoku Mori
The game teaches every technique in this order, each with a worked example and three puzzles of its own. Lesson puzzles are kept apart from the daily ones, and any lesson can be revisited.
Keep reading
All eight: Single candidate · Hidden single · Locked candidates · Naked pair · Hidden pair · Naked triple · Hidden triple · X-Wing