The New Sudoku Players' Forum

[Yogi]

I haven't seen much discussion about 17-Clue Puzzles. I think they are interesting becase they are an ideal training ground for new players to get used to solving puzzles with just the basic techniques, which should build confidence and interest. 17s aren't particularly hard and I never have to use pencilmarks or a computer to solve them. Here are a few:
000000021700060000490000000000070900003800000020000000960000800000302000000100000
000000021800040000000000060090200000700000400000501000015000000000030900602000000
000000023000500080000100000020000900000400100580000000600009500000020070001000000
000000023300010000000500060400000700000106000000200000092000100000040800060000000
The other thing I have wondered about is why 17s are not particularly hard, even though they have the minimum number of clues. I assume it's becase for then to be solvable at all (to a unique solution) there must necessarily be some fairly obvious early moves. That's what I've found, anyway. We heard recently that a study had proved that there are no 16-clue puzzles with unique solutions. Has anyone heard of any studies being done on 17s, looking at the degree of difficulty?

[pjb]

Not all 17s are trivial. Try this one (number 7 from the Top95):
6.2.5.........3.4..........43...8....1....2........7..5..27...........81...6..... (ED=9.0/1.2/1.2)
I'm sure there are plenty of 17s harder than this.
Phil

[champagne]

Not all 17s are trivial. Try this one (number 7 from the Top95):
6.2.5.........3.4..........43...8....1....2........7..5..27...........81...6..... (ED=9.0/1.2/1.2)
I'm sure there are plenty of 17s harder than this.
Phil

That one is one of the hardest of the 49157 known 17 clues puzzles.

Only 3 of them reach the rating 9.0 using serate as reference. To give an idea, that rating is a kind of logarithmic scale and the highest known rating is 11.9.

Yogi, you are right, the reason is that to have a valid puzzle with 17 clues, you have constraints leading ot a relatively easy puzzle.
Most of these puzles could be proposed in newspapers with to-days levels of difficulty.

[pjb]

Champagne, Thanks for pointing this out. I've only seen the couple of 17 clue puzzles in the top95 collection, and imagined that among the 40+ thousand others there would be quite a few with higher ratings.
Phil

[JC Van Hay]

6 singles; {(48)B6, 1B8, 3B168, 5B39, 6B2, 7R24} -> 29 exclusions

Code: Select all

+------------------------+---------------------+------------------------+
| 6      489(7)   2      | 1489-7  5     49-7  | 1389    19(7)    39    |
| 1789   89(57)   15789  | 1789    169   3     | 189(6)  4        2     |
| 13789  489(7)   13489  | 14789   1469  2     | 189(6)  19(567)  9(56) |
+------------------------+---------------------+------------------------+
| 4      3        5679   | 1579    2     8     | 169     1569     569   |
| 789    1        56789  | 34579   349   45679 | 2       3569     48    |
| 289    89(256)  5689   | 13459   1349  4569  | 7       13569    48    |
+------------------------+---------------------+------------------------+
| 5      489(6)   134689 | 2       7     149   | 349(6)  9(6)     39(6) |
| 279    49(267)  4679   | 3459    349   459   | 459(6)  8        1     |
| 139    49       1349   | 6       8     1459  | 3459    2        7     |
+------------------------+---------------------+------------------------+


[XWing(7r13c28)=HT(257-6)r268=6r7c2-6r7c789=6r8c4-6r23c7=HP(56-7)r3c89=7r1c8]-7r1c46; 4 singles; HP(27-469)r8c12=6r7c2; stte

[Yogi]

Thanx everyone for your comments on 17s. Seems that generally they are good fodder for newbies, but there can be a few really hard ones. The puzzle pjb offered took me a while.