Pointing Pair in Sudoku: Clear a Row or Column
A box and a row overlap in three cells. When a box's candidates for a digit all sit in that overlap, the box decides something about the row. Cells are named by row and column: r1c2 is row 1, column 2.
Step 1 of 4
The box points along the row
Box 1 is the top-left box. Its 8 can only go in the ringed cells, r1c2 and r1c3, and both are in row 1. Whichever of them gets the 8, row 1's 8 is inside box 1.
So no cell of row 1 outside box 1 can be an 8. This is a pointing pair: a box's candidates for one digit lie in one row or column, and clear that digit from the rest of the line. Here r1c5 and r1c8 lose their 8.
Use the pointing pair
You don't need to know which of the two cells holds the 8. It's enough that the 8 is in row 1, inside box 1. The rest of row 1 is cleared of 8s.
Your move
Clear the 8 from row 1 outside box 1, then place the digit that is left.
Which way it points
Box 1's 8 is in r1c2 or r1c3. Which cells lose their 8?
Find the pointing pair
Every empty cell has its candidates pencilled in, and none has just one. Look box by box for a digit whose candidates line up in a single row or column.
Your move
Find the pointing pair that unlocks a digit, then place it.
What you learned
- If a box's candidates for a digit all lie in one row or column, that line's digit is inside the box.
- Clear the digit from the rest of the row or column, outside the box.
- It works with two cells or three, as long as they share the line.
In this course
Unit 1The rules
Unit 2Solving techniques
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