How to Solve Sudoku: Hidden Single
A digit can go in only one cell of a box (or row, or column). That cell must be that digit.
Also called process of elimination. On Puzzle Lounge it appears from Easy up.
1See it step by step
- Look at the top-left box (it has no 6 yet)
- 6 goes in one of the 5 empty cells
- Look at the 6s on the board (6 cannot go in the same row or column)
- The other cells share a row or column with a 6 (it cannot go in the cells joined by lines)
- 6 can only go here (● = a cell where 6 can go)
- So this cell is 6 (6 is placed at row 1, column 1)
This is Easy No.1, partly solved.
2How to find it
- Pick a box (or row, or column) and a digit it does not have yet.
- See where that digit is on the board, and rule out the cells in the same row or column.
- When only one cell is left, write the digit in.
Things to watch
- This technique is easiest to spot from a box. It is the one you will use most.
- The trick is to search one digit at a time. Go through 1 to 9 in order.
Read the full explanation
Every box, row and column holds 1 to 9 once each. If a digit not yet placed has only one possible cell in that box (or row, or column), that cell must be that digit.
Suppose a box does not have 6 yet. 6 must go somewhere in this box.
Go through the empty cells of the box one by one. 6 cannot go in a cell whose row or column already has 6.
Rule those out and only one cell is left for 6. That cell is 6.
The top-left box has no 6 yet. The other empty cells share a row or column with the 6s at row 7, column 3, row 2, column 9 and row 3, column 4, so 6 cannot go there. The cell left, row 1, column 1, is 6.
3Other techniques
Naked SinglePointingClaimingHidden 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.