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11 votes
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Anna and Boris play the Red Blue game

That score is attainable with:
ralphmerridew's user avatar
4 votes
Accepted

Yet another pentomino puzzle

I was curious what could possibly be so unusual in the solution. I adapted a program I had for solving pentominos and came up with.
Florian F's user avatar
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3 votes

Pawns and a chessboard with no three aligned

Before this question gets lost in oblivion I would like to give my own solution. I like it because Proof of validity:
Florian F's user avatar
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4 votes
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Rooks covering Dark Squares on a Chessboard

daw's user avatar
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2 votes

Coloring of a 5 x 5 chessboard

You can find the minimum number of monochromatically-cornered rectangles via integer linear programming. Define the following sets: $\text{CELLS} = \{1,\dots,5\} \times \{1,\dots,5\}$ is the set of ...
RobPratt's user avatar
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19 votes
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Coloring of a 5 x 5 chessboard

Borrowing ideas from both @Gareth and @xnor: WLOG one column has at least 3 black squares. Discard the 2 other rows. If any of the 4 other columns has more than 1 black square we are done. We are left ...
loopy walt's user avatar
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12 votes

Coloring of a 5 x 5 chessboard

Here's an argument that (I think) is entirely different from xnor's. (I don't claim that it's better. It feels a bit more straightforward to me.) Each column is either majority-black or majority-white....
Gareth McCaughan's user avatar
7 votes

Coloring of a 5 x 5 chessboard

Consider the 5 rows. Take one color, say white, and for each row, note the white cells and write down every pair of their column indexes. For example, if in the first row, cells 2, 4, and 5 are white, ...
xnor's user avatar
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