Sudoku Solving Techniques, Easy to Hard

Every puzzle here has exactly one solution, and it can be found by logic alone. These techniques, in order, solve the vast majority of Easy to Hard puzzles.

Scan for hidden singles

Pick a number and look at one 3×3 box: if every other cell in that box is ruled out for that number by the rows and columns crossing it, the number must go in the one cell left. Repeat for each number and box — on Easy puzzles this alone often finishes the grid.

Naked singles

Look at a single empty cell and list what it can’t be from its row, column and box. If only one digit is left, that’s the answer.

Use pencil notes

On Medium and Hard, turn on Notes and mark the candidates in each empty cell. Placing a number here clears that number from the notes of every related cell automatically, so new singles appear as you go.

Pairs

If two cells in the same row, column or box can only be the same two numbers, those numbers must go in those two cells — so erase them from every other cell in that unit.

Pointing

If a number’s only possible cells in a box all sit in one row or column, it must go in that row or column within the box — so it can be removed from the rest of that row or column outside the box.

Speed for the leaderboard

The weekly and daily boards rank by time. Scan with hidden singles first, and only start full pencil notes once the easy placements run out.

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