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Magnets (Horseshoes) (1007)
Instruction:
The grid is partitioned into some regions of two square cells each and some 2×2 regions of four square cells each (note that only region borders are drawn). Put "positive" (+) and "negative" (–) symbols into some cells, at most one symbol per cell, such that each region either is completely filled with symbols or no symbols at all. If a 2×2 region is filled with symbols, it must contain two "positive" symbols that touch along an edge and two "negative" symbols that touch along an edge. In all other cases, adjacent cells must not contain the same symbol.
The numbers above and to the left of the grid indicate the exact number of symbols of the specified type that must be placed in each column or row, respectively. If a number is not given, there might be any number of symbols of the specified type.