How to Solve Sudoku: Claiming
In a row (or column), the places for a digit all fit inside one box. Then that digit can be removed from the other cells of that box.
Also called box-line reduction. On Puzzle Lounge it appears from Medium up.
1See it step by step
- A board full of notes. Look only at the 7s (the small digits are the notes, or candidates)
- ● = a cell where 7 can go (notes other than 7 have been removed)
- In row 4, 7 has only these 2 places
- Both are inside the centre box (7 goes in the part of this row that lies in this box)
- The centre box's 7 is used up in this row (a box holds only one 7)
- So the other 7s in the box can be removed (7 goes from row 6, column 5)
This is Hard No.48, partly solved.
2How to find it
- Write out your notes (candidates).
- Pick a row (or column) and see whether any digit's candidates all fit inside one box.
- If they do, remove that digit from the other cells of that box.
Things to watch
- All the candidates in the row (or column) must be in the same box.
- You can only remove it from cells of that box outside that row (or column).
Read the full explanation
When all of a digit's candidates in a row (or column) lie inside one box, the digit must go in that part of the row. So it can be removed from the other cells of the same box.
This is Pointing the other way round. Suppose that in a row, 7 can go in only 2 cells, and both are in the same box.
7 must go somewhere in this row, so this box's 7 falls inside this row.
A box holds only one 7. So 7 cannot go in the other cells of the same box.
In row 4, the candidates for 7 are only at row 4, column 5 and row 4, column 6, both in the centre box. The centre box's 7 falls inside this row, so 7 can be removed from the candidates at row 6, column 5, elsewhere in the box.
3Other techniques
Hidden SingleNaked SinglePointingHidden PairHidden TripleCage Combinations (Killer)Rule of 45 (Killer)Naked PairNaked TripleX-WingXY-WingSwordfishSkyscraper2-String KiteXYZ-WingW-WingJellyfish
For the basics and how to use notes, see how to solve sudoku, with tips. If you get stuck, the game's hints guide you step by step, starting with where to look.