Sudoku

Hey Boomingaway~ Thanks for reminding me that guessing is better than wasting time and it’s OK to miss a puzzle every now & then. (IS it OK? You’re talking to a former crossword junkie. JK-- it’s totally OK! Sure it is…) Well, maybe when I move up another 5000 places, it won’t be such a big deal. If I continue moving up 120 a day for a while, I’ll be 8thousand something by next week. Woohoo!

Don~ I’m sorry you also had to experience the trauma of accidentally *giving up* a game when you could have completed it! And thank you in advance if you can put into words any of the logic you use in solving your puzzles. There are plenty of Sudoku instructions that give the obvious basics, but the more you play, the more you realize there are strategies you can use to solve more quickly, especially when you are looking at a sea of empties. Of course my “hints” might seem obvious to a genius who just looks at the grid and senses what to put where.

Here's one of mine--first a vocab of terms as I use them--I know they're not official terms:

SQUARE: Houses one number
BLOCK: 1 of 9 in the Grid--each block has 9 squares
LINE: Composed of 9 squares, veritcal or horizontal, with or without numbers
EMPTY: A square without a number
LINE-UP: A line housing at least 2 numbers

My Hint: A LINE-UP WITH NUMBERS SPREAD OVER 2 BLOCKS CAN HELP YOU FILL IN THE EMPTIES OF THE 3RD BLOCK ~ Paricularly helpful when you first open the puzzle:

Let's say you have 4 random numbers in the middle line of 2 blocks-- the numbers can have empties between them-- If NONE of those 4 #s are present in the 3rd block and ONLY IF you have EXACTLY 4 empties on either side of the middle line in that 3rd block, you can then automatically fill in the empties with those 4 numbers. --Of course, when filling in those empties, you are taking into account the numbers already present in the surrounding blocks, which helps to eliminate while filling in.

OK, it's a lot easier to see it in your head than to describe it-- and if you were able to follow it, you may think my "hint" is completely obvious! Please feel free to point out flaws. That's all for now.

~Val

Hi, Val. I am not sure there are any official terms for the sudoku grid. I tend to use terms more closely related to mathematics because that is where I have spent most of my life. Here is how I use words to describe things in Sudoku:

SQUARE or GRID refers to the entire 9 x 9 game board.
MINISQUARE or MINIGRID refers to one of the nine 3 x 3 subsets outlined within the grid.
CELL refers to any entry in the grid, blank or not.
ROW refers to the set of nine cells in a horizontal line.
COLUMN refers to the set of nine cells in a vertical line.

I number the rows and columns from 1 - 9 starting in the upper left corner and can locate any cell by simply giving its row number and column number.

Let's use the screenshots on the Sudoku home page for examples and discussion as much as possible so we can all tell what we are describing.

To get started with that, look at the center screenshot and locate the cell at row 6 column 7; it has a 1 in it. Now, let's make a new shorthand notation. Instead of writing "row 6 column 7", write (6,7), so cell (6,7) contains a 1. To continue, (6,8) contains 2 and (6,9) contains 3. This leads me to a new term: BAR. A BAR is a row or column in a minigrid that has all three cells filled in.

I use bars to do something similar to what Val was describing. Using this bar, look across the rest of the rows in this puzzle. In row 4, we find 7, 1, 5, and 6. Our bar contains 1, so 5, 6, and 7 must go in row 5 in the minigrid with the bar. Since 7 is alreeady in place and there is a 6 in column 8, we can fill in all three of these numbers exactly. (Note that this also tells us exactly what three numbers go in the top three cells of this minigrid.) If we had not been able to fix them exactly, I would have penciled them in as best I could because these numbers cannot go any place else on this row. In the other minigrids where the numbers are missing, they must go on row 6. Doing a similar thing with the numbers in row 5, namely 4 and 8, we find they must be in row 4 in the minigrid with the bar and in row 6 in the other minigrids where they are missing. Realizing that there is a bar in row 4 in the left minigrid, we can do the same reasoning there. The result is that most of rows 4, 5, and 6 can be filled in and the remaining cells penciled in fairly quickly.

This has gotten a lot longer than I expected, so I will leave you with this one for now and do more later.

Don

Hey Don~ I will reread your notes carefully after I print up the screen shot. Any suggestions for improvement in strategy are sincerely welcome-- so thank you. The math terms are appropriate and yes, it's challenging to write Sudoku directions concisely.

I found yesterday's genius puzzle to be BRUTAL-- is it possible they are a little harder this week?! I tried to forget about it but it just annoys me to not be able to finish it. Pulled it out last night, limped to the finish line and got 4 next-day points--

Hi. Val. From what I have seen, the stated level of difficulty and the experienced level of difficulty do not always coincide. There are days that the Hard or Genius seems easier than the Easy or Medium. The stated difficulty being based only on the number of cells filled in the beginning is not really an accurate measure of difficulty, in my opinion.

Another thing I do when I seem to have all of the easy things filled in is look for rows, columns, or minigrids that have four or fewer free cells. I will pencil in all of these. Sometimes while trying to pencil something in, I find only one possibility for an entry and this sets off a cascade of entries throughout. In the example I used above, column 5 would be a place to start with this if there were nothing else to do. Also, the top right and the bottom left minigrids would be other places to start.

Another thing I pick up is relations like we see in the bottom middle minigrid. Ignore the minigrid to the left of it for this purpose. What I see is 6 and 8 in column 5 and also in row 7. What this does is tell me that only (4,7) and (6.9) are possible locations for 6 and 8 in the bottom middle minigrid. This then would leave only three possible numbers for the remaining three cells in that minigrid.

That should give you a bit more to think about. I will try to write down more later.

Don

Hi, Val. I just realized that I never completely answered a question you asked earlier. The people on my list that have no highlight color are people who do seem to be regularly earning points in that I have not noted any as having gone for a seven day stretch without earning any points, but they are also not maintaining a pace that would approach 50 points per day. As a result, these are people who will eventually be overtaken by those who strive to maintain as close to a 50 point per day average as possible.

Hope this helps.

Don

Hi Don~ Your last hint about the intersection of pairs is a good one-- the one posted @ 5:28, although I think you meant to say 7/4 & 9/6-- and not something I consciously look for. I'll use that next time I'm solving.

I agree that the level of actual difficulty in solving depends more on the numbers given and the relationship between those numbers rather than the number of empty cells. All 4 of today's puzzles were a welcome relief after the past couple of days!

Hi, Val. You're correct. It should have been (7,4) and (9,6).

Don,

Wow - thanks so much for posting your score spreadsheet. That is facinating.

And excellent catch on my username. vadhopper and vadhopper 9 are indeed both me!


Val - a thought on hard puzzles.

I find it fairly common that you must guess sometimes - at least a couple times per week. If I'm cruising, I will often just guess and hope I'm right. If I have to clear the grid start over. and then hit the same point, I will always write the whole puzzle out on a piece of paper (with all the small numbers as well) and then guess again. The hardest puzzles force you to guess at least twice. I think I had to guess three times in few puzzles - but I also think I missed possible eliminations before I guessed - so I was making it harder on myself. It is faster to just keep pushing ahead most of the time. The longest I've spent on a puzzle is about 50 minutes with this technique.


Great chat.

It seems to me that you shouldn't have to guess. I don't play every day, so I can't say with 100 percent certainty, but I have never had to guess to complete a puzzle. Some of the 'breakthrough fill-ins', in what apeears a deadlocked grid, take several smaller eliminations to break. I find the solve times pretty consistent: Easy average 5 mins, Medium average 5-7 mins, Hard average about 12-15 mins and genius about 15-17 mins. Difficult to describe strategies, so not sure how to give advice.

After thinking a little, I can say that I tend to look at each 9x9 as a whole. Keeping the missing #'s in my head and using clues from surrounding grids to slot the numbers or make small # notes.