dailysudoku.com

[pat1m]

I inputted the following puzzle into the Draw feature, when I got stuck. According to the hint, the next move would be a 7 in r3c5. Why a 7 there and not in r1c5? Would someone be able to explain?
This is what I had:


6.....3......9 | 25.....2478.........48 | ..58 ...1 .....78
7..145...14 | 6.......348.....13489 | 589 ..34 .....2
8..145.....2 | 59.....347.......1349 | ....6 ..34 ....79
__________________________________________
9......2......8 | 4........5...............6 | ...3......7......1
1......7......5 | 3........9...............2 | ...4......8......6
4......6......3 | 8........1...............7 | ...2......9......5
__________________________________________
2......9......6 | 1.......38.............38 | 7......5.......4
3....14....14 | 7..........6..............5 |89......2 ......89
5......8 .....7 | 29......24.............49 | 1......6.......3

[AZ Matt]

I don't know if this is the fastest way to get to 7 in r3c5, pat1m, but it is the most obvious:

There is a type-1 unique rectangle in the r2c23/r8c23. r3c2 must be <5>, otherwise it could be a <1> or a <4>, and the puzzle would not be unique.

You'll get it from there...

Good luck.

Edit: Of course it occurs to me now that the draw hint would not give you the 7 for a clue if it took that route to get there. I will keep working...

[Marty R.]

[keith]

Take a look at row 1. The <4> must be in box 2. So, you can take out all the candidates <4> that are in box 2 and rows 23.

This reveals a naked pair <38> in column 5. You have now eliminated <34> from R3C5. It must be <7>.

And, by the way: Did you notice the Unique rectangle in R28C23? R2C2 must be <5>.

Keith

[ravel]

Alternative:
In row 1 the 4 only can be in column 4 or 6, both in box 2. Therefore you can eliminate it from r23c56 (same box). This gives you the same naked pair 38 in r27c5 in column 5 => r3c5=7.

[keith]

Ravel, and all,

You might enjoy this:

From the posted position, use the UR to set R2C2 = <5>.

Then you have a Type 4 unique loop: The three corners of the old UR and R23C6. This eliminates <4> from R23C6!

Keith

[AZ Matt]

I think I am missing your point, Keith. I see that the <4> must be in either r2c3 and r3c8, or r3c2 and r2c8, but in any event not in r2c56 nor r3c56. That doesn't appear to be what you are refering to.

What is a unique loop?

[ravel]

[keith]

I apologize that my previous post has a sloppy explanation.

Here is the posted position:

[AZ Matt]

Thanks Keith. In the future, I think anytime we see a "super-advanced" solving technique in a puzzle, we should report it, whether it it is necessary to the puzzle or not. I am constantly making puzzles more difficult than they need to be simply because I get bored with the usual stuff, and I wouldn't have it any other way...

[pat1m]

Thank you all. I see the reasoning for the 7 now. I should have caught the row 1, box 2 4's thing. Thanks again. I didn't realize the rectangle 145 14 14 14 box, but now I can add that to the methods to try to solve puzzles