How to solve Sudoku: techniques from basic to advanced

Solve in a loop instead of scanning randomly

A hard Sudoku is rarely solved by one “secret trick.” It is solved by repeating the right layers of deduction in order. Start with naked and hidden singles; when those run out, update candidates, check block–row/column intersections, and only then move to pairs, triples, or advanced patterns.

After every certain digit, restart the cycle from the beginning. An advanced step often opens several new singles; if you keep hunting complex techniques immediately, you may miss simple moves and make your notes heavier than necessary.

• Scan rows, columns, and blocks for naked and hidden singles.
• Only complete Notes in the region that is actually stuck.
• After every major elimination, return to the basic techniques before going deeper.

Use few Notes, but keep them accurate

Candidates are useful only when they reflect the board's current state. If you enter a digit but do not remove related candidates from the same row, column, and block, later patterns may be false. Note quality matters more than note quantity.

When a candidate in a block is restricted to one row or column, you have a locked candidate. When two cells in a region contain exactly the same two digits, you have a naked pair. These are two important bridges from basic solving to Hard Sudoku.

• Use Notes when a cell still has two or more possibilities.
• Update candidates immediately after every new digit.
• Do not eliminate a digit because it 'seems unlikely'; every elimination needs a reason.

When do you need X-Wing and multi-region patterns?

Look for X-Wing only after you are sure naked singles, hidden singles, locked candidates, pairs, and triples are no longer making progress. The pattern uses positions of the same candidate across two rows or two columns to eliminate that candidate from the other intersections.

The important point is to confirm the full structure before eliminating. If either source row still has a third position for that candidate, the X-Wing does not exist. Checking slowly and carefully prevents one mistake from sending the entire deduction chain in the wrong direction.

• Learn one new technique with examples you can verify step by step.
• Do not use an advanced technique just because the puzzle is labeled Hard or Extreme.
• If a deduction chain becomes too long, go back and check your notes and basic patterns.

Practice by technique, not only by time

Speed comes from recognizing patterns faster, not from making speed the only goal. After each game, ask what made you stuck: locked candidates, pairs, X-Wing, or simply a missed single. Choose the next difficulty so that technique appears often enough to practice.

If you need hints constantly, drop one level and practice the process again. When you can solve consistently with very little Undo or hint use, increase the difficulty. This builds more durable progress than jumping straight to Extreme and guessing.