The New Sudoku Players' Forum

[DaiBleacky]

Hello!

This is my first topic. I'm trying to go with the rules, but if i comit any error, i'm sorry.

I Play on the APP by "Brainium". When i'm stucked, i use the tips the app give to me. But i only use this after i understand the strategy involved on the tip. On the case below (Level difcult) i did'nt understanded. Could you help me telling me why i need to do as the tip says?

The app tip says that i need to write "3" on the square "G4". But i dont see it as the unique possibility. Could you help me?

Whithout pencilmarks:

Code: Select all

9 . . | 1 . 5 | . 8 3
. 8 . | . 6 . | . 5 .
. . 4 | 7 3 8 | 9 . .
----------------------
2 6 . | 8 . 7 | . 4 9
. . . | . . . | . . 8
8 4 9 | 3 . 6 | . 2 7
----------------------
. . 2 | 4 7 3 | 8 . .
4 3 8 | 6 9 1 | 2 7 5
7 . . | 5 8 2 | . . 4


With pencilmarks:

Code: Select all

9  27  67   | 1  24 5  | 467  8    3
13 8   137  | 29 6  49 | 147  5    12
56 125 4    | 7  3  8  | 9    16   126
------------------------------------
2  6   135  | 8  15 7  | 135  4    9
13 17  1357 | 29 24 49 | 1356 136  8
8  4   9    | 3  15 6  | 15   2    7
------------------------------------
56 159 2    | 4  7  3  | 8    169  16
4  3   8    | 6  9  1  | 2    7    5
7  19  16   | 5  8  2  | 136  1369 4


Image:

[Pat]

their 3 is indeed correct
but the tip is apparently random
and based on no strategy

to solve this puzzle,
you need the X-wing
(6) columns AH in rows 47

[SpAce]

There's a hidden pair (47) in r12c7 (or G1 and G2 in your coordinate system) which eliminates other candidates from those cells. Alternatively you can make the same eliminations through a naked triple (126) in box 3 [added: or a naked quad (1356) in column 7].

Code: Select all

    A   B    C      D   E   F    G     H     J
  .---------------.------------.-----------------.
1 | 9   27   67   | 1   24  5  | 47-6  8     3   |
2 | 13  8    137  | 29  6   49 | 47-1  5    *12  |
3 | 56  125  4    | 7   3   8  | 9    *16   *126 |
  :---------------+------------+-----------------:
4 | 2   6    135  | 8   15  7  |%135  #4     9   |
5 | 13  17   1357 | 29  24  49 |%1356  136   8   |
6 | 8   4    9    | 3   15  6  |%15    2    #7   |
  :---------------+------------+-----------------:
7 | 56  159  2    | 4   7   3  | 8     169   16  |
8 | 4   3    8    | 6   9   1  | 2    #7     5   |
9 | 7   19   16   | 5   8   2  |%136   1369 #4   |
  '---------------'------------'-----------------'

Hidden Pair (47)r12c7 or Naked Triple (126)b3p689 [or Naked Quad(1356)r4569c7] => -6 r1c7, -1 r2c7

Of course you could use the X-Wing Pat suggested (should be columns AJ(?) rows 37, though), but that's unnecessarily advanced for this puzzle. Either way it's singles to the end.

Code: Select all

    A   B    C      D   E   F    G     H     J
  .----------------.------------.------------------.
1 | 9    27   67   | 1   24  5  | 467   8    3     |
2 | 13   8    137  | 29  6   49 | 147   5    12    |
3 |*5(6) 125  4    | 7   3   8  | 9     1-6 *12(6) |
  :----------------+------------+------------------:
4 | 2    6    135  | 8   15  7  | 135   4     9    |
5 | 13   17   1357 | 29  24  49 | 1356  136   8    |
6 | 8    4    9    | 3   15  6  | 15    2     7    |
  :----------------+------------+------------------:
7 |*5(6) 159  2    | 4   7   3  | 8     19-6 *1(6) |
8 | 4    3    8    | 6   9   1  | 2     7     5    |
9 | 7    19   16   | 5   8   2  | 136   1369  4    |
  '----------------'------------'------------------'

X-Wing (6)c19/r37 => -6 r37c8

PS. In future posts, please define the coordinate system you're using if it's not what's standard on this forum (rYcX). Otherwise there might be ambiguity about what's rows and what's columns.

[SpAce]

their 3 is indeed correct but the tip is apparently random and based on no strategy

True (*). What's also funny is that placing that 3 doesn't even break the bottleneck. The same hidden pair, naked triple, X-Wing, or something is still needed. Seems like a pretty dumb app.

(*) [Edit: Not true, actually. I guess we both missed the should-have-been-obvious UR (15)r46c47 that does the trick.]

[Pat]

X-wing
(6) columns AH in rows 47


too often now i'm off by 1,
getting old.

(6) c19\r37

and funny indeed that i should use the X-wing at all --
as SpAce showed, b3 {4,7} solves the 6 for r1

[DaiBleacky]

their 3 is indeed correct
but the tip is apparently random
and based on no strategy

to solve this puzzle,
you need the X-wing
(6) columns AH in rows 47

Thank you. It solved the puzzle.

There's a hidden pair (47) in r12c7 (or G1 and G2 in your coordinate system) which eliminates other candidates from those cells. Alternatively you can make the same eliminations through a naked triple (126) in box 3 [added: or a naked quad (1356) in column 7].

It helped me too. Thank you.

PS. In future posts, please define the coordinate system you're using if it's not what's standard on this forum (rYcX). Otherwise there might be ambiguity about what's rows and what's columns.

I'm sorry. Going to do thath next time.

My first objective was to understand the strategy on the tip, but i think the tip was based on no strategy. Even so, i learned a lot with you two. Thank you.

[SpAce]

My first objective was to understand the strategy on the tip, but i think the tip was based on no strategy.

On a second look, that's not entirely true:

Code: Select all

.----------------.------------.-----------------.
| 9    27   67   | 1   24  5  |  467   8    3   |
| 13   8    137  | 29  6   49 |  147   5    12  |
| 56   125  4    | 7   3   8  |  9     16   126 |
:----------------+------------+-----------------:
| 2    6    135  | 8  *15  7  |x*3-15   4     9 |
| 13   17   1357 | 29  24  49 |  1356  136   8  |
| 8    4    9    | 3  *15  6  | *15    2     7  |
:----------------+------------+-----------------:
| 56   159  2    | 4   7   3  |  8     169   16 |
| 4    3    8    | 6   9   1  |  2     7     5  |
| 7    19   16   | 5   8   2  |  136   1369  4  |
'----------------'------------'-----------------'

Unique Rectangle Type 1 (15)r46c57 => -15 r4c7

Like the X-Wing, it's considered a more advanced technique than hidden pairs or naked triples, but it's often easier to spot especially if solving without pencil marks. URs are often available too, and I use them a lot even with basic puzzles if I don't immediately see other moves. In this case it wouldn't have solved the puzzle, though.

[DaiBleacky]

Like the X-Wing, it's considered a more advanced technique than hidden pairs or naked triples, but it's often easier to spot especially if solving without pencil marks. URs are often available too, and I use them a lot even with basic puzzles if I don't immediately see other moves. In this case it wouldn't have solved the puzzle, though.

Yeah. I remamber that the tip said "if this square (r4c7) wasn't '3', the puzzle should have just 2 solutions, one with the '1' and other with '5'." And them completed that square with the "3". And i didn't understanded anything.