4 ms·
Example, in the top-left corner of the board: 2 _ _ R _ _ _ _ R _ _ _ The location to the right of the 2 must be blue. If it's red, then there's no way
by T-hawk 12y ago
Example, in the top-left corner of the board:
2 _ _ R
_ _ _ _
R _ _ _
The location to the right of the 2 must be blue. If it's red, then there's no way for the 2 to see two blues. That's what it means, that that dot is included in every possible solution for the 2.