Expert Sudoku

Sudoku is played on a grid of 9 rows and 9 columns, split into nine 3×3 boxes. Some cells start with a digit (the clues). You fill in the rest.

Expert puzzles start with as few clues as our generator could remove while keeping a single solution.

• Each row holds the digits 1 to 9, each exactly once.
• Each column holds the digits 1 to 9, each exactly once.
• Each 3×3 box holds the digits 1 to 9, each exactly once.
• The clues can't be changed. The puzzle is solved when every cell is filled and no digit repeats in a row, column or box.

Each expert puzzle here gets stuck after singles, pointing and pairs. It needs at least one of: a naked or hidden triple, a naked or hidden quad, or an X-Wing. Of our 1000 expert puzzles, our solver needed an X-Wing in 650 and a naked triple in 338.

Puzzles that need wings, Swordfish or Jellyfish are on the Master level. We don't list puzzles that need trial and error: our own solver, using only named techniques, finished every one, so a logical path always exists.

X-Wing: look at one digit. If on two rows it can only go in the same two columns, the four cells form a rectangle and the digit takes two opposite corners. Either way both columns are used up, so the digit can be removed from those columns everywhere else. It works with rows and columns swapped too.

Triples and quads: three cells of a unit that between them can only hold three digits (not every cell needs all three) lock those digits in, just like a pair. Hidden triples are the same idea from the digits' side: three digits that fit only in the same three cells.

Pick a cell, then a number; Notes switches the buttons to pencil marks (N on a keyboard). On expert puzzles Hint shows the whole pattern, every cell of a wing or fish it reads. Undo takes back any step, and your game is saved in this browser.

Fill in complete notes early. Then always try the easy steps first: after each elimination, look again for singles and pairs before you search for anything bigger.

For an X-Wing, pick the digit with the fewest notes left and look at where it can go on each row and column. For triples, look at units with four to six empty cells.

If you are stuck, Hint names the technique the next step needs and marks its cells, which is a good way to learn the patterns.