当a=-3,A={-3},B={4,1},交集空,并集{-3,4,1}
当a=1,A={-3,1},B={4,1}交集{1},并集{-3,4,1}
当a=4,A={-3,4},B={4,1}交集{4},并集{-3,4,1}
其他情况,A={-3,a},B={4,1}交集空,并集{-3,a,4,1}