had to assume the solution for this puzzle is unique in order to solve it -- I'm wondering if someone else
can find the solution without making that assumption.
Here's how I attacked it. After completing 15 cells and making a few eliminations by means of simple
coloring I arrived at this position.
Code: Select all
4 268 26 68 1 7 3 5 9
356 7 356 346 9 2 1 8 46
368 9 1 3468 48 5 2 47 467
3569 4 3569 59 27 36 8 1 27
1 268 2569 589 2478 46 579 479 3
23589 238 7 1459 248 134 59 6 24
7 1 8 2 6 9 4 3 5
269 5 269 14 3 14 679 279 8
2369 236 4 7 5 8 69 29 1
-- Assume that the solution is unique.
-- If the "8" in column 4 lies in the top center 3x3 box there will be a "non-unique rectangle" fully
formed in r6c4, r6c6, r8c4, & r8c6, with the crucial digit "3" lying in r6c6.
-- In particular, r1c4 <> 8. Assume the converse. Then we have
r1c4 = 8 ==> r3c5 = 4 ==> r3c8 = 7 ==> r5c8 = 4 ==> r5c6 = 6 ==> r4c6 = 3
and this contradicts the uniquity assumption.
Therefore r1c4 = 6 and the rest is just an exercise. dcb