Evil Sudoku Printable

Each puzzle has its own PDF, with one large grid on page 1 and the solution on page 2. Puzzles 1 to 3 are Diabolical, puzzles 4 to 6 are Evil.

• Diabolical Sudoku 1 - 26 given numbers. Our solver needed: XY-Wing.
• Diabolical Sudoku 2 - 28 given numbers. Our solver needed: X-Wing and XY-Wing.
• Diabolical Sudoku 3 - 30 given numbers. Our solver needed: XY-Wing and Swordfish.
• Evil Sudoku 4 - 24 given numbers. Not solved with X-Wing, XY-Wing and Swordfish.
• Evil Sudoku 5 - 25 given numbers. Not solved with X-Wing, XY-Wing and Swordfish.
• Evil Sudoku 6 - 24 given numbers. Not solved with X-Wing, XY-Wing and Swordfish.

There is no official scale for sudoku difficulty, and the same name can describe different levels from one book or website to another. On this page, the level comes from a checking program that solves each grid the way a person does, one technique at a time, starting with the simplest.

• Diabolical (or diabolic) sudoku. Our solver could not finish the puzzle with singles, locked candidates and subsets (pairs, triples and quads). It needed at least one X-Wing, XY-Wing or Swordfish, and the page tells you which.
• Evil sudoku. The program got stuck even with these three techniques. The puzzle still has exactly one solution, but you will need longer chains of reasoning or careful trial and error.

Grids that could be solved with simpler techniques were rejected, whatever their number of given numbers.

• X-Wing. In two rows, a number can only go in the same two columns. It must then sit in opposite corners of that rectangle, so it can be removed from the other cells of those two columns. The same works with rows and columns swapped.
• Swordfish. The same idea as the X-Wing, with three rows and three columns.
• XY-Wing. A cell with two candidates, X and Y, sees a cell with X and Z and another cell with Y and Z. One of these two cells must contain Z, so Z can be removed from every cell that sees both of them.

• Write all the candidates in small numbers in each empty cell: the advanced techniques cannot be seen without them.
• Update the candidates every time you place a number.
• Exhaust the simple techniques first, then look for cells with only two candidates: they are the starting point of an XY-Wing.
• For an X-Wing, pick one number and look for rows or columns where it has only two possible cells.
• Use a pencil and an eraser, and print a second copy before trying a long line of reasoning.

Want more grids, or an easier level to warm up? The free Sudoku generator creates sample puzzles online with their solutions, in several difficulty levels.