The New Sudoku Players' Forum

[m_b_metcalf]

Code: Select all

 1 . 2 . . . 3 . .
 . 4 3 . . . . . .
 5 6 . 1 . . . . .
 . . 1 7 . . 6 . .
 . . . . . 4 . 8 .
 . . . . 5 . . . 9
 7 . . 6 . . 1 . .
 . . . . 8 . . 5 4
 . . . . . 5 . 6 .      one backdoor + singles

1.2...3...43......56.1.......17..6.......4.8.....5...97..6..1......8..54.....5.6.


I think a good place to start looking for a backdoor is to look where an additional clue, with a value that already occurs
frequently, can be strategically placed.

[P.O.]

there are 14 size 1 backdoors in singles:

Code: Select all

n6r2c5 n7r2c8 n1r2c9 n7r3c6 n6r5c1 n1r5c5 n7r5c9
n6r6c6 n1r6c8 n3r8c2 n1r8c6 n7r8c7 n1r9c2 n7r9c5