// X is a good number if after rotating each digit individually by 180 degrees, we get a valid number that is different from X. Each digit must be rotated - we cannot choose to leave it alone. // A ...

An integer x is "good" if rotating each digit individually by 180 degrees results in a valid number that is different from x. - 0, 1, 8 rotate to themselves. - 2 and 5 rotate to each other. - 6 and 9 ...