17-Clue Puzzles

Everything about Sudoku that doesn't fit in one of the other sections

17-Clue Puzzles

Postby Yogi » Wed Feb 17, 2016 9:09 pm

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?
Yogi
2017 Supporter
 
Posts: 81
Joined: 05 December 2015
Location: New Zealand

Re: 17-Clue Puzzles

Postby pjb » Wed Feb 17, 2016 10:52 pm

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
pjb
2014 Supporter
 
Posts: 1576
Joined: 11 September 2011
Location: Sydney, Australia

Re: 17-Clue Puzzles

Postby champagne » Thu Feb 18, 2016 2:32 am

pjb wrote: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.
champagne
2017 Supporter
 
Posts: 5572
Joined: 02 August 2007
Location: France Brittany

Re: 17-Clue Puzzles

Postby pjb » Thu Feb 18, 2016 5:51 am

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
pjb
2014 Supporter
 
Posts: 1576
Joined: 11 September 2011
Location: Sydney, Australia

Re: 17-Clue Puzzles

Postby JC Van Hay » Thu Feb 18, 2016 8:36 am

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
JC Van Hay
 
Posts: 642
Joined: 22 May 2010

Re: 17-Clue Puzzles

Postby Yogi » Mon Feb 22, 2016 6:33 am

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.
Yogi
2017 Supporter
 
Posts: 81
Joined: 05 December 2015
Location: New Zealand


Return to General