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This site contains three different sudoku variants: Code-Doku and Cube Sudoku, and a new set of variants featured on the home page and posted daily on Sudoku of the Day.

Code-Doku puzzles blend the logical challenge of normal sudoku puzzles with a surprise message that is revealed as you work toward a solution. Instead of using the digits one through nine, Code-Doku puzzles use letters. Other letter-based puzzles such as Go Doku (or Godoku), Sudoku Word or Wordoku have a hidden word, often down the diagonal. Code-Doku puzzles have shaded squares that contain the hidden message. When you have determined the solution to the puzzle, the letters in the shaded squares will spell out the hidden message.

Cube Sudoku puzzles are formed on the six faces of a cube. Each face has a 4×4 grid. The sixteen values must be placed so that each value appears exactly once on each face. In addition, the rows and columns on each face extend all the way around the cube. Each of the sixteen values must also be placed so that each value appears exactly once in each of the twelve strips.

The Sudoku of the Day page features sudoku puzzles in a variety of novel configurations. Like Cube Sudoku, the rows and columns of these puzzles may curve, so that the same strip may pass through one box as a row, but pass through another box as a column.

If you'd like to be notified when new puzzles are posted, just send me an e-mail at the address below. For more information about these puzzles, please check out the Code-Doku and Cube Sudoku pages. Good Luck!

Current Code-Doku Puzzle

This puzzle was suggested by Arnie Miller in San Mateo, California.

   S    I C    B    
   N E         H    
 B C    H          P
     C    B      P  
     B         N    
   H      I    E    
 A          B    N S
     P         I A  
     S    P I    B  

A Special Treat

by Steve Schaefer

Place each of the letters of BE SPINACH exactly once in each row, column and 3×3 box. When you have completed the puzzle, the shaded squares can be read left to right, then top to bottom to form a phrase describing a special treat.


Difficulty: Easy

Here is a print-friendly version of this puzzle and a solution.

Other difficulties:
All of these can be solved using the sudoku placement rules alone, and they all have the same hidden message. Choose a puzzle difficulty that fits your interest, or solve the easy puzzle then try a harder one after you know the message.

  • Medium — Requires no advanced techniques
  • Hard — Cannot be solved with elimination alone
  • Tricky — Requires something beyond row/box and column/box interactions
  • Harder — Cannot be solved with elimination alone
  • Fiendish — Requires something beyond row/box and column/box interactions
  • Extreme — Requires advanced techniques beyond forced chains

Cube Sudoku

The image below is the current "Easy" Cube Sudoku puzzle. You can get a larger version of this puzzle, the solution, and more difficult puzzles at the main Cube Sudoku page.

Difficulty: Easy
Top: .....25C..9..70D Left: ....E3A61.D4.F.. Front: 98....D...6..... Right: ........C..7E.B. Bottom: F.1...4.A....B.. Rear: .3..8.2.A.F4...7

Other Sudoku Puzzles and Links

Sudoku of the Day -- Daily puzzles, mostly with 3x3 boxes connected by curving row/columns.
Code-Doku -- The main page for code-doku puzzles (with previous puzzles).
Cube Sudoku -- The main page for cube sudoku puzzles.
Code-Doku Archive -- Previous code-doku puzzles from this site.
Code-Doku FAQ -- More information about Code-Doku puzzles and how to solve them.
Top Notch -- The only other source for Code-Doku puzzles.
Top 50 Sudoku Sites -- A collection of links to sudoku puzzles, solvers, games and more.
Beginner's Introduction to Sudoku -- This is all you need for the easy and moderate puzzles when I give a full set of difficulty levels for a codedoku.
Sudoku Solving Techniques -- This site presents more advanced techniques for solving tricky, fiendish and extreme puzzles.
Sudoku Methods -- My own description of sudoku methods. It's not as polished, but it includes some methods that do not apply to the classic 3×3 grid of 3×3 boxes.

Please send responses to my email address is mathrec at this domain