Sudoku tips: solve faster, with fewer mistakes

Getting started on a puzzle

1. Start with the most common digit. Count which digit appears most among the clues and scan that one first. The more copies on the board, the more cells they block, and the more likely a box has only one place left for it.

2. Scan by digit, not by cell. Asking where the 4 goes in this box is much faster than asking what goes in this cell. Sweep each digit across all nine boxes before moving to the next digit.

3. Use rows of three boxes. Take three boxes side by side. If two of them have a 6, in two different rows, the third box must have its 6 in the remaining row. That often leaves only one or two cells.

4. Follow up every placement. Each digit you place changes one row, one column and one box. Look at those three first. Moves come in chains, and the next link is nearly always next to the last.

Using notes well

5. Do not note too early. Filling the whole grid with notes at the start is slow and hides the easy moves. Place every single first, then note what remains.

6. Note cells with two candidates first. They are the most useful ones. Two cells in a unit with the same two notes form a naked pair, and a cell that drops to one note is solved.

7. Keep notes up to date. When you place a digit, remove it from the notes in its row, column and box straight away. Stale notes are the main cause of mistakes in the harder puzzles. Sudoku Clan can remove them for you automatically.

When you are stuck

8. Change the question. If you have been asking where digits go, ask what cells can hold. Find a cell that sits in a busy row, column and box, and count what is left for it.

9. Check lines, not just boxes. Most people over-scan boxes and under-scan rows and columns. A row with three gaps is a small problem: three missing digits, and usually at least one of them is blocked from two of the gaps.

10. Look for locked candidates. If a digit inside a box can only go on one row, it cannot be anywhere else on that row. This is the pointing pair, and it is the usual key to an expert puzzle.

11. Never guess. A wrong guess does not show itself for a long time, and by then you cannot tell which digits to trust. Use a hint instead: in Sudoku Clan the hint names the technique and explains the step, so you learn the move for next time.

Getting faster

12. Practise at one level until it is dull. Speed comes from recognising patterns without effort. Play easy puzzles until you finish them without stopping, then move up. Racing other people helps too: in multiplayer Sudoku you solve the same puzzle as your opponent, so you see straight away how your pace compares.

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