The New Sudoku Players' Forum

[Ocean]

Thanks claudiarabia for the many contributions, which have also stimulated lots of discussions!

I have updated the first post of this thread with all puzzles posted so far, but many are still in the waiting box: "Puzzles not yet characterized". Here is a new one from me, with a small xy-ring:

Code: Select all

#
# 4-Ring (18 clues with rotational symmetry)
#
 *-----------*
 |...|...|..1|
 |...|.2.|.34|
 |5..|..6|...|
 |---+---+---|
 |...|..7|6..|
 |.8.|...|.2.|
 |..4|3..|...|
 |---+---+---|
 |...|4..|..9|
 |65.|.1.|...|
 |7..|...|...|
 *-----------*


[re'born]

Here is a new one from me, with a small xy-ring:

Code: Select all

#
# 4-Ring (18 clues with rotational symmetry)
#
 *-----------*
 |...|...|..1|
 |...|.2.|.34|
 |5..|..6|...|
 |---+---+---|
 |...|..7|6..|
 |.8.|...|.2.|
 |..4|3..|...|
 |---+---+---|
 |...|4..|..9|
 |65.|.1.|...|
 |7..|...|...|
 *-----------*


Excellent puzzle, Ocean! It should qualify for the effortless extreme thread as well.

[Ocean]

Excellent puzzle, Ocean! It should qualify for the effortless extreme thread as well.

Thanks for the evaluation. And true, such puzzles also fit in the 'effortless extreme thread'. My solver/analyzer finds these patterns easily in a batch of puzzles, and I can sort out those satisfying for instance "in addition to basics, only one xy-ring needed, and no equally long xy-chain does the same elimination job". Hope to improve the tool to handle some of the more complicated cases, to give assistance with the "to be categorized later" collection.

Another one with 18 clues:

Code: Select all

#
# 4-ring: (8 possible eliminations)
#
 *-----------*
 |...|...|...|
 |...|.1.|..2|
 |.34|..5|.6.|
 |---+---+---|
 |...|..3|..7|
 |8..|...|..1|
 |1..|9..|...|
 |---+---+---|
 |.5.|4..|93.|
 |7..|.2.|...|
 |...|...|...|
 *-----------*

The xy-ring is visible already from start (may then eliminate 11 candidates) and the puzzle is then solved with singles + one naked pair. If basic techniques (up to triples) are applied first, 8 candidates are eliminated by the xy-ring.

[claudiarabia]

Code: Select all

19 clues, horizontal and vertical symmetry, it is the first of this kind that I see:
Code:
"Glasses"
 . . . . . . . . .
 . . 1 . . . 2 . .
 . 3 . 4 . 5 . 6 .
 . . . . 1 . . . .
 6 4 . . 7 . . 3 2
 . . . . 8 . . . .
 . 8 . 3 . 6 . 4 .
 . . 9 . . . 7 . .
 . . . . . . . . .  Mauricio

According to SE this sudoku can be solved with a bi-directional cycle and an XY-Wing and a forcing chain. You can avoid the forcing chain while adding another bi-directional cycle including r2c128, r8c12,r9c1. When starting the cycle with 5 in r2c1 (right, clockwise) you will 9 in r2c8. When you start with 4 in r2c1 (left, anticlockwise), you will get a naked pair of 59 in r9c28. In both directions 59 in r2c9 are eliminated.

Code: Select all

 

 *--------------------------------------------------------------------*
 | 8      59     456    | 1      36     2      | 3459   579    34579  |
 | #45    #569   1      | 7      36     8      | 2     #59    34-59   |
 | 7      3      2      | 4      9      5      | 8      6      1      |
 |----------------------+----------------------+----------------------|
 | 29     7      35     | 26     1      34     | 4569   8      4569   |
 | 6      4      8      | 5      7      9      | 1      3      2      |
 | 29     1      35     | 26     8      34     | 4569   579    45679  |
 |----------------------+----------------------+----------------------|
 | 1      8      7      | 3      2      6      | 59     4      59     |
 | #35   #56     9      | 8      4      1      | 7      2      36     |
 | #34    2      46     | 9      5      7      | 36     1      8      |
 *--------------------------------------------------------------------*


Then an xy-wing in r2c19, r8c1 will solve the puzzle finally.

claudia

[Eioru]

5 kind of rating of Bidirectional Y-Cycle
The Bidirectional Y-Cycle isn't the hardest solving method in some puzzles.

6.6 There is 8 "If...then..."
8.......7.9....85...5287.....68.53.4..3...9....83.42...8.6315...21....4.5.9.....1
6.7 There is 10 "If...then..."
8.......6.9.....1....456.....41.95....7...3....86.32.....267....1.....3.5.......9
6.8 There is 12 or 14 "If...then..."
..1..3.5.7..4..9...3......44...2..8....9.5....8..7...6.......4...2..6..1.6.7..2..
6.9 There is 16 or 18 "If...then..."
8...9...1.9.3.8.4.............4.7.3.2.......6.6.9...1...........4.7.5.9.1...8...2
7.0 There is 20 or 22 "If...then..."
9...8...6.8...4.7...........1.4.5...2.......1.4.7.6.2...........7...8.5.6...9...3