The New Sudoku Players' Forum

[amirzadeh]

Here is the original puzzle

Code: Select all

 *-----------*
 |.8.|...|.23|
 |..5|.31|...|
 |74.|...|...|
 |---+---+---|
 |39.|...|...|
 |.2.|...|.8.|
 |...|4..|.79|
 |---+---+---|
 |4.2|..7|9..|
 |6..|1.9|..7|
 |9..|2..|.6.|
 *-----------*

so far

Code: Select all

 *-----------*
 |189|...|.23|
 |265|.31|...|
 |743|...|...|
 |---+---+---|
 |39.|...|..2|
 |52.|...|.8.|
 |816|4..|.79|
 |---+---+---|
 |4.2|..7|9..|
 |6.8|1.9|2.7|
 |97.|2..|.6.|
 *-----------*

Now from what the solvers tell me, r1c7 [4567] and r9c7 [3458] have a pair Hidden pair that lets me ~3 r9c7, which releases the next set of numbers. The question is why?

Thanks.

Aram

[wapati]

A much simpler approach is to note that c8 has threes only at r7 and r8.
That means r7c8 is 3 or r8c8 is 3. r9c7 cannot be three.

There is a similar exclusion, look at column 7 in the middle box.
The only threes in the box are in column 7, thus there can be no threes
in c7 in the box above and below.

As to the hidden 45 pair, I don't see it nor can I disprove it.

[Carcul]

r1c7 [4567] and r9c7 [3458] have a pair Hidden pair

There is no hidden pair in those cells. What you have is: a naked single in r9c3 ("1"), and locked candidates in box 6 ("3"), which allow us to exclude "3" from r9c7. The type-1 UR then later solved the puzzle.

Carcul

[amirzadeh]

A much simpler approach is to note that c8 has threes only at r7 and r8.
That means r7c8 is 3 or r8c8 is 3. r9c7 cannot be three.

There is a similar exclusion, look at column 7 in the middle box.
The only threes in the box are in column 7, thus there can be no threes
in c7 in the box above and below.

As to the hidden 45 pair, I don't see it nor can I disprove it.

This did the trick for me. I should have noticed that '3' was only present in c7r456 so that it would ~3 c7r789.

Thank you.