This can be done in constant time using math, but brute force is enough to get the first two test cases. The answer is just #unpainted rows * #unpainted columns, or
$(R - r) \cdot (C - c)$ Another way to see this is to use inclusion/exclusion: The number of black squares painted by the rows is: # rows painted (r) x total number of columns (C) The number of black squares painted by the columns is: # columns painted (c) x total number of rows (R) Overlaps were double counted, so we need to subtract r*c The answer is then
$RC - (rC + cR - rc)$ which is the same as the above answer
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