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Daily Sudoku Answer 



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Feb 12 - Super Hard
Puzzle Copyright © Kevin Stone

Share link – www.brainbashers.com/s078410



Reasoning 



R2C6 can only be <6>

R9C1 can only be <3>

R1C5 can only be <8>

R3C1 can only be <8>

R1C1 can only be <2>

R2C4 can only be <4>

R3C5 can only be <1>

R7C1 can only be <5>

R5C1 can only be <7>

R5C3 can only be <1>

R1C9 is the only square in row 1 that can be <5>

R3C2 is the only square in row 3 that can be <3>

R4C6 is the only square in row 4 that can be <5>

R4C5 is the only square in row 4 that can be <7>

R5C6 is the only square in row 5 that can be <3>

R7C8 is the only square in row 7 that can be <3>

R7C2 is the only square in row 7 that can be <8>

R8C8 is the only square in row 8 that can be <5>

R8C2 is the only square in column 2 that can be <6>

R8C4 can only be <1>

R9C3 can only be <4>

R8C6 can only be <2>

R8C7 can only be <4>

R6C6 can only be <1>

R8C3 can only be <7>

R2C3 can only be <9>

R2C2 can only be <7>

R1C3 can only be <6>

R1C7 can only be <9>

Squares R7C5 and R9C5 in column 5 form a simple naked pair. These 2 squares both contain the 2 possibilities <69>. Since each of the squares must contain one of the possibilities, they can be eliminated from the other squares in the column.

R5C5 - removing <6> from <246> leaving <24>

R6C5 - removing <9> from <249> leaving <24>

Squares R7C5, R7C9, R9C5 and R9C9 form a Type-1 Unique Rectangle on <69>.

R9C9 - removing <69> from <269> leaving <2>

R9C7 can only be <6>

R9C5 can only be <9>

R7C9 can only be <9>

R7C5 can only be <6>

The puzzle can be reduced to a Bivalue Universal Grave (BUG) pattern, by making this reduction:

R6C8=<48>

These are called the BUG possibilities. In a BUG pattern, in each row, column and block, each unsolved possibility appears exactly twice. Such a pattern either has 0 or 2 solutions, so it cannot be part of a valid Sudoku

When a puzzle contains a BUG, and only one square in the puzzle has more than 2 possibilities, the only way to kill the BUG is to remove both of the BUG possibilities from the square, thus solving it

R6C8 - removing <48> from <248> leaving <2>

R6C2 can only be <9>

R6C5 can only be <4>

R2C8 can only be <8>

R4C8 can only be <6>

R5C7 can only be <8>

R2C7 can only be <2>

R4C4 can only be <9>

R3C8 can only be <4>

R5C9 can only be <4>

R5C4 can only be <6>

R5C5 can only be <2>

R3C9 can only be <6>

R6C4 can only be <8>

R4C2 can only be <2>



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