Look at the board below, focusing on row 4. There are six empty cells in it: 42, 43, 51, 52, 53 and 62 (Please see Sudoku Rules and Terminology on how to locate cells). Notice there are two 4s around row 4, 54 can point out 51, 52 and 53 because they are in the same box, and 32 can point out 62 because they are in the same column, but we still don't know where 4 goes since there are still two cells 42 and 43 left in row 4.
Well, turns out, not only cells can be pointers, units can be pointers too! Let's look at box 1, notice the empty cells in box 1 form a letter T. Now beam light from 32 to box 1, the three cells 11, 12, and 13 that form the upper part of the T are pointed out, leaving the two cells 15 and 18 that form lower part of the T. We don't know which one is 4 but we sure know that 4 in box 1 must be in column 2, so now box 1 can be used as a pointer, which can point out 42 in our target row 4, leaving 43 the only cell left. Click on the board, if you haven't yet, to see the animations.
Another example, box pointer pointing to column.
More examples, here is a box pointer pointing to box:
Of course columns and rows can be unit pointers too, here is an example of column-row pointing:
Another example of column-row pointing:
A special case of column-row pointing, cross pointing:
An example with a box pointing, a column-row pointing and a cross pointing:
The beauty of unit pointers is, they rely:
That's it for unit pointing, now you can use it to solve Medium level Sudoku puzzles.
Sudoku Rules and Terminologies
Technique No.1 Pointing Out - Easy Level
Technique No.2 Pointing Out - Medium Level
Technique No.3 Fitting In - Medium Level
Technique No.4 Fitting In - Hard Level
Technique No.5 Pointing Out - Hard Level
Technique No.6 Pointing Out - Expert Level
Technique No.7 Fitting In - Expert Level
No comments:
Post a Comment