Only one cell in this row or column can hold that digit.
Technique 3 in the order the hint searches · difficulty Medium · up to hidden singles
This time you take hold of a line. Count how many cells in this row could take an 8; if there is only one, that cell is the 8. The logic matches the box version exactly; only the direction you look changes.
Take one line and count its nine cells
You come here when box scanning stalls. Starting with lines that have only two or three empty cells is quickest. Try the digits missing from that line one at a time and something usually catches straight away.
How the hint says it
In row 2, 8 can only go in r2c5. Every other cell there is blocked.
Every line holds that digit exactly once
An 8 must appear somewhere in this row's nine cells. If only one cell can take it, that cell is the 8. Same reason as the box, with only the unit changed.
The hint checks boxes first and moves to lines when that fails, because that is the order people learn them in.
Puzzles that need this technique
Four puzzles with a spot where nothing moves until you use Hidden Single (Line). Press a number to play it.
- Practice 1 ·
1-8307283 - Practice 2 ·
1-6614566 - Practice 3 ·
1-5486088 - Practice 4 ·
1-2100654