dailysudoku.com

[buettner]

I have been doing sudokus for about 2 months now, but I am still having trouble resolving triples. This is unfortunate since resolving triples has been a positive boon for solving puzzles. Here is an example from a recent puzzle that I don't understand.

45 1 8 3 26 9 24 7 2456

The way I see it, there are two possibilities for a triple; 1) using 245 and 2) using 246

Using 245, the 6 can be eliminated from cell 9, which means that cell 5 must be 6; but this is incorrect.

Using 246, the 5 can be eliminated from cell 9, which means that cell 1 must be 5, and this is correct.

I cannot see why the 246 choice should be any better than 245, but that's the one that works. I'd be very interested to hear why that is the case.

As an aside, I wonder about how the degree of difficulty is determined for sudokus. I have solved puzzles from the London Daily Telegraph and the LA Times that were rated as diabolical with some difficulty, but the puzzles in my local paper (San Francisco Chronicle) give me a lot more trouble starting on Thursday where they are rated as 4 out of 6, and by Saturday when they are rated as 6 out of 6, I really have trouble. Anyway I just wonder if they is some sort of standardized, objective way of rating difficulty.

[ravel]

There is no triple in this line. A 5 in cell 9 still is possible this way:
4 1 8 3 6 9 2 7 5
For a hidden triple there must be 3 numbers, that can only go to the same 3 cells.

There is no standardized rating system. Any rating is subjective, because different people prefer a different order of applying techniques. But there is common agreement, that the rating system of many sudoku sites is not good. Mostly many easy puzzles are rated as hard as real hard ones.