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Showing posts with label rearrangement. Show all posts
Showing posts with label rearrangement. Show all posts

Saturday, April 21, 2018

Collinear marbles

From OSP SMA 2018. On a 200x200 checkerboard, we place red and blue marbles, at most 1 marble per cell. Two marbles are considered "collinear" if they are on the same column or row. For each red marble, there are exactly 5 collinear blue marbles, and for each blue marble, there are exactly 5 collinear red marbles. Find the maximum number of marbles on the board.