The New Sudoku Players' Forum

[Montmorency]

Hi!

This is probably quite simple if you're experienced but I can't get around it.

Please help me with the next number and a nice and simple explanation of how you came to that conclusion.

Thanks in advance!

[SpAce]

This is probably quite simple if you're experienced but I can't get around it.

Please help me with the next number and a nice and simple explanation of how you came to that conclusion.

Instead of a direct answer I'll give you a hint: study Unique Rectangles. This one has the simplest Type 1 available, and you're quite right that an experienced player can see it in one glance. If you find and execute it, the rest is easy. Other possibilities are a W-Wing or an XY-Wing (actually two), but they're a little trickier to spot. All are among the simplest and most common non-basic techniques, so you'll definitely need them a lot if you want to solve non-basic puzzles. You'll learn more if you try to find them yourself here, but ask again if you can't.

Code: Select all

1...7.9...3.5..1....2....35.6.34....2..6.1..3....28.9.38....5....9..7.4...6.5...9

.-----------.--------------.------------.
| 1   4   5 | 2    7    3  | 9   6   8  |
| 68  3   7 | 5    68   9  | 1   2   4  |
| 68  9   2 | 14   168  46 | 7   3   5  |
:-----------+--------------+------------:
| 9   6   1 | 3    4    5  | 28  78  27 |
| 2   7   8 | 6    9    1  | 4   5   3  |
| 4   5   3 | 7    2    8  | 6   9   1  |
:-----------+--------------+------------:
| 3   8   4 | 9    16   26 | 5   17  27 |
| 5   12  9 | 18   3    7  | 28  4   6  |
| 7   12  6 | 148  5    24 | 3   18  9  |
'-----------'--------------'------------'

[Leren]

145273968.375.9124.92...735961345...2786914534537286913849..5..5.9.37.467.6.5.3.9

Code: Select all

*------------------------------------*
| 1   4   5 | 2   7   3  | 9   6  8  |
| 68  3   7 | 5   68  9  | 1   2  4  |
| 68  9   2 | 14  168 46 | 7   3  5  |
|-----------+------------+-----------|
| 9   6   1 | 3   4   5  | 28  78 27 |
| 2   7   8 | 6   9   1  | 4   5  3  |
| 4   5   3 | 7   2   8  | 6   9  1  |
|-----------+------------+-----------|
| 3   8   4 | 9   16  26 | 5   17 27 |
| 5  a12  9 | 18  3   7  |b28  4  6  |
| 7   2-1 6 | 148 5   24 | 3  c18 9  |
*------------------------------------*

There is an XY Wing in cells a-b-c that removes 1 from r9c2 and solves the puzzle.

In words, if a is not 1 it is 2, so b is not 2 and so it is 8, so c is not 8 it is 1. So either a or c is 1 so r9c2 is not 1.

If you want to learn more aboout XY Wings look here.

Leren

[SpAce]

There is an XY Wing in cells a-b-c that removes 1 from r9c2 and solves the puzzle.

Yeah, but it's the hardest to spot of the three possibilities I mentioned, so why single that out? For a human player the UR is clearly the easiest (I saw it immediately), and the W-Wing probably comes next for most people (because you can look for two identical bivalue cells). An XY-Wing is a simple pattern but still it has almost never simply caught my eye, and probably never will. What's easy for software is not necessarily obvious for a human, and vice versa.

[Montmorency]

This is probably quite simple if you're experienced but I can't get around it.

Please help me with the next number and a nice and simple explanation of how you came to that conclusion.

Instead of a direct answer I'll give you a hint: study Unique Rectangles. This one has the simplest Type 1 available, and you're quite right that an experienced player can see it in one glance. If you find and execute it, the rest is easy. Other possibilities are a W-Wing or an XY-Wing (actually two), but they're a little trickier to spot. All are among the simplest and most common non-basic techniques, so you'll definitely need them a lot if you want to solve non-basic puzzles. You'll learn more if you try to find them yourself here, but ask again if you can't.

Code: Select all

1...7.9...3.5..1....2....35.6.34....2..6.1..3....28.9.38....5....9..7.4...6.5...9

.-----------.--------------.------------.
| 1   4   5 | 2    7    3  | 9   6   8  |
| 68  3   7 | 5    68   9  | 1   2   4  |
| 68  9   2 | 14   168  46 | 7   3   5  |
:-----------+--------------+------------:
| 9   6   1 | 3    4    5  | 28  78  27 |
| 2   7   8 | 6    9    1  | 4   5   3  |
| 4   5   3 | 7    2    8  | 6   9   1  |
:-----------+--------------+------------:
| 3   8   4 | 9    16   26 | 5   17  27 |
| 5   12  9 | 18   3    7  | 28  4   6  |
| 7   12  6 | 148  5    24 | 3   18  9  |
'-----------'--------------'------------'

Perfect, thanks! Easy enough now. Have to study up on some basic techniques.