Only one digit can go in this cell.
Technique 1 in the order the hint searches · difficulty Easy · naked singles only
Start from the cell. Cross off every digit already placed in the twenty cells it can see — eight in its row, eight in its column, the remaining four in its box. Once eight of the nine are gone, the one left is the answer.
Look for the cell with only one gap left
Start where the digits are dense. A cell sitting where a busy row, column and box all overlap is the cell with the most digits blocking it. Early in a puzzle these are hard to see; after a few placements they start arriving in runs.
How the hint says it
Nothing but 2 can go in r1c5. Between them, its row, column and box block the other eight digits.
Cross off until one remains and there is nothing else it can be
The whole rule of sudoku is “1 to 9 once each in every row, column and box”. If eight digits are blocked, placing the ninth is the only move available. That is elimination, not a guess.
A puzzle that finishes on this technique alone is labeled Easy. Difficulty here is measured by the technique a puzzle demands, not by how many clues were removed.
Puzzles that need this technique
Four puzzles with a spot where nothing moves until you use Naked Single. Press a number to play it.
- Practice 1 ·
0-9435761 - Practice 2 ·
0-8871522 - Practice 3 ·
0-8307283 - Practice 4 ·
0-7743044