Unable to complete puzzle # 22 in Second-Degree Black Belt Sudoku, I turned to http://www.sudokusolver.co.uk which is able to:
- use Guess-and-Check soduku solving steps
- determine whether a sudoku puzzle has a unique solution
Tuesday, September 22, 2009
Sudoku Solver .. by logic
Unable to complete puzzle # 22 in Second-Degree Black Belt Sudoku, I turned to http://www.sudokusolver.co.uk which is able to:
Second-Degree Black Belt Sudoku
I purchased a new sudoku puzzle book, Second-Degree Black Belt Sudoku (by Frank Longo) from a big-box book seller. Why? Possibly I'm worried that my favorite sudoku puzzle book (New York Post series by Wayne Gould) was nearly full. The good news is that Second-Degree Black Belt Sudoku has:
The bad news about Second-Degree Black Belt Sudoku is that:
- more difficult puzzles compared to the New York Post series by Wayne Gould
- more puzzles; 300 versus 150
The bad news about Second-Degree Black Belt Sudoku is that:
- paper quality is not compatible with using an eraser
- top and bottom margins are smaller leaving less room for margin notes
Sunday, November 30, 2008
Speed and what to do before adding a unique solution.
Does one solution strategy (or method) have a speed advantage? I try strategies which minimize the number of hints (pencil marks), like finding a completed 3x1 and working in that line or lucky number (see below). Adding more pencil marks is how a computer would solve a puzzle and I am not a computer.
What about peeking at the solution? Peeking slows me down. Usually, all I need is to re-confirm that I have a unique solution. In other words, before adding the solution, I re-confirm that the number is not already used in the 3x3 or 9x1. For me, time spent double checking whether the solution is unique usually prevents an error--fixing broken puzzles slows me down and errors usually end in discarding the puzzle.
In what order should I fill in the solutions? Do other cells carry less risk in making an error? If possible, when choosing between multiple solution strategies, I try to choose the least complex logic. Occam's razor (14th-century English logician and Franciscan friar, William of Ockham)--"... one should not increase, beyond what is necessary, the number of entities required to explain anything."
What about peeking at the solution? Peeking slows me down. Usually, all I need is to re-confirm that I have a unique solution. In other words, before adding the solution, I re-confirm that the number is not already used in the 3x3 or 9x1. For me, time spent double checking whether the solution is unique usually prevents an error--fixing broken puzzles slows me down and errors usually end in discarding the puzzle.
In what order should I fill in the solutions? Do other cells carry less risk in making an error? If possible, when choosing between multiple solution strategies, I try to choose the least complex logic. Occam's razor (14th-century English logician and Franciscan friar, William of Ockham)--"... one should not increase, beyond what is necessary, the number of entities required to explain anything."
Tuesday, October 28, 2008
newspaper and in-flight magazines; pen or pencil
Recently, I have been sudoku puzzling using newspaper and in-flight magazines--again. As the newspaper is not suitable for pencil and eraser--well, I have been using a pen. For easy puzzles, pen is not a problem, but I am re-learning that my preference is for high quality paper with lots of room, especially when it comes to difficult puzzles. The big-box booksellers are not stocking the difficult New York Post puzzles. Luckily, I discovered more New York Post book choices on amazon.com, and the New York Post Platinum Su Doku looks promising--I think I'll order that.
Saturday, January 5, 2008
my experience with paper based sudoku puzzles
Here is my experience with paper based sudoku puzzles. I started with a glossy in-flight magazine puzzle then onto newspaper puzzles and finally to several paperback books. These books progressed from easy to fiendish in puzzle difficulty. Warning: Once you have mastered the puzzle rules, you may become addicted to the thrill of reaching the puzzle tipping point.
Pencil versus Ink - My preference is a mechanical pencil with an eraser like the BIC 0.7mm #2. In my enthusiasm, I make mistakes. Alternatively, I make a mess of things and then move onto the next inexpensive puzzle.
Magazine versus Newspaper versus Paperback Book - My preference is a paperback book of puzzles like the New York Post Su Doku series. Quality paper does not tear easily and does not clog the eraser. If you are a commuter and right handed, then do not be surprised that you are completing only right hand pages while holding the paperback book with your left hand.
Margins versus NO Margins - My preference is for lots of margin space (white space outside of the grid) to write margin notes and strategy notes to myself. Other than this blog, the margins are where I gather my thoughts or strategies.
Large Squares versus Small Squares - My preference is large square that easily hold four hints (aka pencil marks).
Morning versus Afternoon versus Evening - My preference is to work in the morning while listening to the radio. Listening to the radio and working with puzzle numbers are nearly compatible tasks. Setting a fixed time aside to puzzling each morning is one way of managing puzzle frustration. After puzzle fatigue sets in, then more continuous time spent on the puzzle leads to more frustration and not a puzzle solution. Finally, the self imposed fixed time rule leaves time for other relationships, work and hobbies.
Margin Notes - The outer edges (white space outside of the grid) of the my puzzle contain hints too. Margin notes define a hint or hints that are confined to a 3x3 and a line and help reduce the number of hints per cell to four or less. The margin notes also help me finish puzzles in more than one sitting. Warning: Review your hints to see that only one line in a 3x3 contains a particular margin note and that outside the 3x3 the particular hint is excluded in that line.
Circling - Cells in my puzzle are circled when the number of hints are exactly two. Especially within a 3x3 or line, circling helps me reduce the number of hints per cell. Also, circling helps me evaluate the puzzle for twins in a 3x3 or line. Warning: Review circled cells carefully as an error may reveal a unique solution!
Beginning Phase - I do not repeat a particular hint more than three times in a 3x3 assuming the particular hint is also contained in the same line. Typically, notes within the grid are know as pencil marks. However, I place additional notes outside the grid - what I refer to as the margins (white space outside of the grid). These margin notes are reminders that a hint is restricted to a line within a 3x3. In other words, scanning down that line, the hint can not be used in other 3x3's or other lines in the same 3x3. In this way, I avoid puzzle clutter and information overload. This phase may be marked by finding a lucky number. In other words, sometimes a particular solution can be discovered in almost all of the 3x3's.
Middle Phase - The middle phase is defined by reviewing margin notes, correcting logic errors, removing hints, adding hints, circling, discovering twins and discovering triples. However, the middle phase uses all the beginning phase rules without exception. Warning: This is the longest phase where I use my focused attention. It may be necessary to put the puzzle down if I have reached puzzle fatigue.
Brute Force Phase - At some point, I relax some of the clutter control rules, but I selectively choose what 3x3 to repeat the particular hint more than three times. Rare Number: I begin adding extra hints in a 3x3 or line that contains a rare number. A rare number is a particular solution that appears no more that once in the puzzle. Perhaps I can find two different rare numbers and work where lines passing through those rare numbers intersect. Tight spaces: Also, I begin adding extra hints in a 3x3 or line that contains tight spaces. A tight space is a 3x3 or line that contains 3 blanks (6 solutions).
End Phase - At some point I reach the tipping point. In other words, I reach a point where I have overcome any logic challenges that the puzzle has to offer - the puzzle is completed conceptually. Enjoying the glow of success, I get ready to do the end zone dance - spike the ball - high five or whatever mythical celebration I have in mind.
Pencil versus Ink - My preference is a mechanical pencil with an eraser like the BIC 0.7mm #2. In my enthusiasm, I make mistakes. Alternatively, I make a mess of things and then move onto the next inexpensive puzzle.
Magazine versus Newspaper versus Paperback Book - My preference is a paperback book of puzzles like the New York Post Su Doku series. Quality paper does not tear easily and does not clog the eraser. If you are a commuter and right handed, then do not be surprised that you are completing only right hand pages while holding the paperback book with your left hand.
Margins versus NO Margins - My preference is for lots of margin space (white space outside of the grid) to write margin notes and strategy notes to myself. Other than this blog, the margins are where I gather my thoughts or strategies.
Large Squares versus Small Squares - My preference is large square that easily hold four hints (aka pencil marks).
Morning versus Afternoon versus Evening - My preference is to work in the morning while listening to the radio. Listening to the radio and working with puzzle numbers are nearly compatible tasks. Setting a fixed time aside to puzzling each morning is one way of managing puzzle frustration. After puzzle fatigue sets in, then more continuous time spent on the puzzle leads to more frustration and not a puzzle solution. Finally, the self imposed fixed time rule leaves time for other relationships, work and hobbies.
Margin Notes - The outer edges (white space outside of the grid) of the my puzzle contain hints too. Margin notes define a hint or hints that are confined to a 3x3 and a line and help reduce the number of hints per cell to four or less. The margin notes also help me finish puzzles in more than one sitting. Warning: Review your hints to see that only one line in a 3x3 contains a particular margin note and that outside the 3x3 the particular hint is excluded in that line.
Circling - Cells in my puzzle are circled when the number of hints are exactly two. Especially within a 3x3 or line, circling helps me reduce the number of hints per cell. Also, circling helps me evaluate the puzzle for twins in a 3x3 or line. Warning: Review circled cells carefully as an error may reveal a unique solution!
Beginning Phase - I do not repeat a particular hint more than three times in a 3x3 assuming the particular hint is also contained in the same line. Typically, notes within the grid are know as pencil marks. However, I place additional notes outside the grid - what I refer to as the margins (white space outside of the grid). These margin notes are reminders that a hint is restricted to a line within a 3x3. In other words, scanning down that line, the hint can not be used in other 3x3's or other lines in the same 3x3. In this way, I avoid puzzle clutter and information overload. This phase may be marked by finding a lucky number. In other words, sometimes a particular solution can be discovered in almost all of the 3x3's.
Middle Phase - The middle phase is defined by reviewing margin notes, correcting logic errors, removing hints, adding hints, circling, discovering twins and discovering triples. However, the middle phase uses all the beginning phase rules without exception. Warning: This is the longest phase where I use my focused attention. It may be necessary to put the puzzle down if I have reached puzzle fatigue.
Brute Force Phase - At some point, I relax some of the clutter control rules, but I selectively choose what 3x3 to repeat the particular hint more than three times. Rare Number: I begin adding extra hints in a 3x3 or line that contains a rare number. A rare number is a particular solution that appears no more that once in the puzzle. Perhaps I can find two different rare numbers and work where lines passing through those rare numbers intersect. Tight spaces: Also, I begin adding extra hints in a 3x3 or line that contains tight spaces. A tight space is a 3x3 or line that contains 3 blanks (6 solutions).
End Phase - At some point I reach the tipping point. In other words, I reach a point where I have overcome any logic challenges that the puzzle has to offer - the puzzle is completed conceptually. Enjoying the glow of success, I get ready to do the end zone dance - spike the ball - high five or whatever mythical celebration I have in mind.
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