Expert sudoku

About expert sudoku

Expert sudoku puzzles start with 23 to 28 numbers, and each needs at least one technique beyond pairs. Triples and quads extend the pair idea: three cells in a row, column or box that between them can only hold three numbers claim those numbers, and the same goes for four cells and four numbers. Hidden triples and quads are the mirror image: three or four numbers that fit in only the same three or four cells.

The other Expert technique is the X-Wing. Suppose a number can go in only two cells in each of two rows, and those cells sit in the same two columns. The number must take one corner of that rectangle in each row, so those two columns get their copy of it from these two rows. It can then be removed from every other cell in both columns. The same works with rows and columns swapped.

These patterns only show up in complete notes, so fill in every candidate before you go looking. Each puzzle here was kept because its hardest step is one of these techniques, no more and no less.

Sudoku levels

• Easy sudoku: 36 to 40 numbers to start, singles only.
• Medium sudoku: 30 to 35 numbers to start, singles only.
• Hard sudoku: 26 to 31 numbers to start, locked candidates and pairs.
• Expert sudoku: 23 to 28 numbers to start, triples, quads and the X-Wing.
• Master sudoku: 22 to 27 numbers to start, wings and the Swordfish.
• Extreme sudoku: 21 to 26 numbers to start, beyond all of the above.
• Sudoku: carry on at your last level

How to play

Fill the grid so that every row, every column and every 3 by 3 box holds the numbers 1 to 9 once each. Every puzzle has exactly one solution, and you can always reach it by logic, without guessing.

1. Select a cell, then tap a number. A wrong number turns red and counts as a mistake. Three mistakes end the game, but once per game you can take a second chance: the last mistake is removed and you carry on.
2. Turn on Notes to pencil in the numbers a cell could hold. When you place a number, it is removed from the notes in its row, column and box.
3. Undo takes back your last move, as many times as you like. Erase clears a wrong number or a cell’s notes. Numbers you placed correctly stay put.
4. Stuck? Hint shows the next step and explains it. Press it again to fill the cell.
5. The clock stops while you’re paused or in another tab. Your game is saved as you go, so you can come back to it later.
6. Settings lets you turn off the mistake check, the limit, the highlights or the timer. Statistics shows your wins, best times and streaks for each level.

Keyboard

Questions

What’s the difference between the levels?

Each level asks for harder reasoning. Easy (36 to 40 numbers to start) and Medium (30 to 35) only need you to find, again and again, the one cell where a number must go. Hard adds locked candidates and pairs, Expert triples and the X-Wing, and Master the Swordfish and the XY-Wing. Extreme puzzles need steps beyond all of these.

What does Hint do?

It finds the easiest next step on the board, names the technique and explains it, and highlights the cells and candidates involved. Press Hint again, or Apply, to fill the cell. A hint counts even if you fill the cell yourself, and that cell earns no points. If a number on the board is wrong, the hint points to it first.

How is the score worked out?

Each correct number earns points, more on harder levels and more the sooner it follows your last one. A number that completes a row, column or box earns five times as much for each one it completes. Hints earn nothing, and a cell only scores once, even if you undo it. With the mistake check turned off, there is no score.

Where is my game kept?

Only in this browser, one game per level, along with your statistics and settings. Nothing is sent anywhere, and clearing your browser’s site data removes them.

More to play

• Queens Puzzle: Place one queen in every row, column and colored region.
• Minesweeper: Open every square without a mine. The numbers tell you where they are.
• All puzzles
• El Trivia home