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Nuraf (859)
Instruction:
Shade some empty (non-numbered) cells black (leaving the other cells white) so that the grid is divided into non-overlapping regions; cells of the same color are considered in the same region if they are adjacent along edges. Each white region must have exactly two given numbers; the area of the region (in cells) must be between those two numbers (therefore, not equal to either of those two numbers). All black cells must be in the same region. No 2×2 group of cells can be entirely shaded black.