## How would you rate this puzzle?

Everything about Sudoku that doesn't fit in one of the other sections

### How would you rate this puzzle?

Code: Select all
2 . 5 | . . . | . 1 9
9 . . | . . . | . 4 .
4 6 . | 8 1 . | . . 2
-------+-------+------
. . . | 1 7 4 | . . .
. . . | . 8 . | . . .
. . . | 6 2 5 | . . .
-------+-------+------
7 . . | . 4 2 | . 6 8
. 4 . | . . . | . . 5
3 9 . | . . . | 2 . 4

This puzzle needs *nothing* but naked and hidden singles until only 22 cells are left. No need to use pencil marks until then. At that point, fill in pencil marks in *only* the cells that you can narrow down to exactly 2 candidates. You'll find an xy-type forcing chain only 5 cells long -- then nothing but net.

Though forcing chains are an advanced tactic, I think even a relative novice could crack it in a short while. (Pappocom rates it as invalid.) It would be nice to be able to create/find puzzles like this at will. It's easier to practice finding forcing chains when you know they are there.
tso

Posts: 798
Joined: 22 June 2005

I can't resist Sherlocking instead ...
The candidates for row 5 and row 6 after the simpler moves are
Code: Select all
15   7    46   | 9    8    3    | 456  2    16
18   3    49   | 6    2    5    | 47   89   17
row 5 has only three allowable possibilities:
Code: Select all
1    .    4      .    .    .      5    .    6       (A)
5    .    6      .    .    .      4    .    1       (B)
5    .    4      .    .    .      6    .    1       (C)  <--
row 6 has only two allowable possibilities:
Code: Select all
1    .    9      .    .    .      4    8    7       (D)  <--
8    .    4      .    .    .      7    9    1       (E)
(C,D) is the only compatible pair.
r.e.s.

Posts: 337
Joined: 31 August 2005