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Newsletter #1 – August 2009
With a couple of months delay, I’ve created my first newsletter. It is available here.
These newsletters will be sent out monthly by e-mail to those who sign up. You can sign up by submitting your e-mail address in the box in the left-hand navigation pane (above the book cover pages) or by sending me an e-mail.
My first Nurikabe puzzle (a difficult one)
Another addition to my portfolio of various number/logic puzzles are Nurikabe puzzles.
I think these puzzles are being undeservedly somewhat neglected in the puzzle world and I intend to change that. The number of solving techniques and approaches that can be found in Nurikabe puzzles far exceeds any other puzzle type. For me it was a challenge programming a solver and a generator of Nurikabe puzzles, much more than programming all other puzzles so far.
Goal:
For each cell, determine if it must be white (draw a circle in it) or black (paint it).
There are two types of Nurikabe jargon:
1) White cells are walls, black cells are a maze.
2) White cells are islands, black cells are a stream.
Folks, I’d really like to hear what you think of Nurikabe puzzles in general and about this particular puzzle (the difficulty in first place). So, please do post your comments!
The Rules of Nurikabe
1. Cells with numbers (initial clues) are always white. 2. 2×2 (or bigger) blocks of black cells are not allowed. 3. All black cells must be connected orthogonally (horizontally or vertically). In other words: there is a maze between the walls. Or: A stream runs between the islands. 4. The initial numbers (clues) indicate how many white cells are orthogonally connected with the cell that contains the number (including that cell). In other words: the numbers indicate how big each island is; or again, how big each wall is. 5. White cells that “belong” to two different clues must be separated by black cells. In other words: two islands cannot touch each other, there must be some water between them. Or, two walls must be separated by the maze. 6. Nurikabe puzzles can be of any size. And finally, here is the puzzle. I’m still working on automagically determining the difficulty of these puzzles, but I think this one is quite tough. Nurikabe 12×12 for July 20, 2009. Click on the puzzle thumbnail to access the puzzle.
Posted in Free sample puzzles, General, Puzzle variants
Tagged IQ, rules, solving technique, technique
14 Responses
How to solve Hitori: basic techniques
Solving Hitori puzzles is about recognizing patterns. I will show you some examples of those patterns. They can be split into two groups, one of those that depend solely on the initial positioning of numbers, and another group of patterns that depend on the black and white cells which have been painted in the solving process.
One trivial advice that you should always keep in mind: if a cell cannot be black, it must be white! And vice versa. From this comes one simple solving technique: when you conclude that a cell must be painted, circle the numbers in all four adjacent cells to indicate that they must be left unpainted. Now, back to the patterns:
When you have 2 same numbers adjacent to each other in a corner, you can circle at least one other number. Why? It is easy to see that the 1 cannot be black, because one of the 4s must be black. If the leftmost 4 were black, the 1 would be adjacent to it. If the rightmost 4 were black, the 1 couldn’t be black because those two black cells would isolate the other 4 in the corner, which is against the 2nd rule of Hitori. Got it?
Here are some other similar patterns that occur in corners:
And here are some other examples for you to practice:
A number squeezed between two same numbers must be white! If it were black, it would eventually cause two black cells to be adjacent, which is not allowed.
Oh, and don’t be put off by three same numbers adjacent in a row or column. The same rule applies.
No room for three Another very common pattern is when two same numbers are adjacent to each other and there is another one in the same row/column. Obviously, one of the adjacent 3s will have to be white (they can’t both be black). Whichever one it is, the 3rd 3 in the same column will have to be black, as you can’t have two 3s in one column.
Those were the basics. That’s how you start solving any given puzzle. In a few days, I will post some more complex patterns that are used in the more difficult of puzzles.
Corners
Check the corners first. Here is an example:When you have 2 same numbers adjacent to each other in a corner, you can circle at least one other number. Why? It is easy to see that the 1 cannot be black, because one of the 4s must be black. If the leftmost 4 were black, the 1 would be adjacent to it. If the rightmost 4 were black, the 1 couldn’t be black because those two black cells would isolate the other 4 in the corner, which is against the 2nd rule of Hitori. Got it?
Here are some other similar patterns that occur in corners:
And here are some other examples for you to practice:
Squeezed in the middle
This is probably the most common pattern in Hitori puzzles.A number squeezed between two same numbers must be white! If it were black, it would eventually cause two black cells to be adjacent, which is not allowed.
Oh, and don’t be put off by three same numbers adjacent in a row or column. The same rule applies.
Elimination
By the way, once you’ve circled a number, make sure to eliminate all other occurrences of the same number in the same row and column:
No room for three Another very common pattern is when two same numbers are adjacent to each other and there is another one in the same row/column. Obviously, one of the adjacent 3s will have to be white (they can’t both be black). Whichever one it is, the 3rd 3 in the same column will have to be black, as you can’t have two 3s in one column.
Those were the basics. That’s how you start solving any given puzzle. In a few days, I will post some more complex patterns that are used in the more difficult of puzzles.
Posted in Puzzle variants, Solving tips
Tagged EASY, HITORI, how to solve, IQ, solving technique, technique
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CalcuDoku clarification
In order to avoid any further confusion with KenKen(R) and KenDoku(TM) trademarks of Nextoy, LLC, I have changed the name of these puzzles to CalcuDoku.
This name is also used by other publishers but it is not trademarked.
Weekend Special – CalcuDoku Samurai (Gattai-5) puzzle
This is my largest CalcuDoku puzzle so far. Previously I published a CalcuDoku Samurai 7×7, but this time the puzzle is even larger:
8×8 CalcuDoku Samurai for Saturday, February 28, 2009.
CalcuDoku for Saturday, Feb 28, 2009
Difficulty: IQClick on the puzzle thumbnail to access the puzzle.
The Reduced Operators version of CalcuDoku is here.
These puzzles are also available to newspapers, magazines and other publishers. Be the first to have my CalcuDoku puzzles printed!
You can use my CalcuDoku Calculator to help you out with the possible combinations for a cage.
Enjoy! Questions, comments and suggestions are more than welcome!
Difficulty: IQClick on the puzzle thumbnail to access the puzzle.
The Reduced Operators version of CalcuDoku is here.
These puzzles are also available to newspapers, magazines and other publishers. Be the first to have my CalcuDoku puzzles printed!
You can use my CalcuDoku Calculator to help you out with the possible combinations for a cage.
Enjoy! Questions, comments and suggestions are more than welcome!
Posted in CalcuDoku, Free sample puzzles, Samurai sudoku
Tagged calcudoku, calcudoku calculator, calculator, gattai, OPERATORS, REDUCED, samurai, suggestions, Weekend Special
3 Responses
Hitori
UPDATE: After some debate with udosuk (see comments), I’ve decided to adopt the rule that every cell must be either black or white, it can’t be left “undecided”. I’ve changed the original puzzle accordingly so you can download it now.
At the end of last year, I announced that I will be introducing more types of number-logic puzzles on this site.
First up – HITORI puzzles.
Goal:
Eliminate duplicate numbers from each row and column by shading them black.
Rules of Hitori:
1. Two black cells must not touch each other horizontally or vertically. Diagonally is Ok. 2. All white cells must constitute one continuous area. In other words, there must be a path between any two white cells, without crossing “the wall” of black cells. Think of it as a maze. Hitori puzzles can be of any size, from a tiny 4×4 (or even 3×3) to any size you can imagine. Today I’m presenting you a rather large one, 15×15 in size. You can read how to solve Hitori by following that link.Hitori 15×15 for February 7, 2009.
Click on the puzzle thumbnail to access the puzzle.
Posted in Free sample puzzles, Puzzle variants
Tagged HITORI, how to solve, rules, UPDATE
7 Responses
Sudoku Forum
Unfortunately the Sudoku forum on this website has been deleted. Perhaps it will be back at some point. Until then, feel free to comment bellow every post and page.
Sudoku Straights
It’s only Wednesday, but I decided to present you with another Sudoku Straights puzzle. Remember that they are shown every Friday on the Daily Sudoku variants page.
The rules:
1. Use numbers 1-9. Numbers cannot be repeated in rows/columns.
2. There are no nonets (3×3 boxes) like in other Sudoku puzzles.
3. Black cells do not contain numbers. Therefore, not all numbers 1-9 will appear in all rows/columns. (Be careful when applying hidden singles!)
4. And the main rule: numbers in one row/column that are between two black cells (or between a black cell and the border) must constitute a sequence, or if you prefer poker (texas hold’em or whatever) terminology, they must constitute a straight. Now, do not confuse this with consecutive sudoku! The numbers can be in any order, adjacent numbers need not be consecutive! Just like in poker.
Sudoku Straights for January 21, 2008.
Click on the puzzle thumbnail to access the puzzle.
Daily Hidoku
As you all may have noticed, I’ve finally started posting Hidoku puzzles on a daily basis!
They can be found every day, Monday to Friday, on the Hidoku page!
