To find the juntion place of two rectangles.
It's like a Category Discussion method. More simplest method?
Let me see STD. I think this problem is a little hard...
First consider the situation without junction
if (E >= C || F >= D || B >= H || A >= G) return sum1 + sum2;
Without junction just compute the (min left - max right) * (min up - max down)
Also sum1 + sum2 may > INT_MAX we need let it minus the overlap part first!