Assume that the total area is never beyond the maximum possible value of int.

 

Credits:
Special thanks to @mithmatt for adding this problem, creating the above image and all test cases

class Solution

{

public:

  int computeArea(int A, int B, int C, int D, int E, int F, int G, int H)

  {

    int x1 = A > E ? A : E;

    int y1 = B > F ? B : F;

    int x2 = C > G ? G : C;

    int y2 = D > H ? H : D;

    int x = x2 - x1, y = y2 - y1;

    int s = ;

    if(x> && y>)

      s = x * y;

    return (C-A)*(D-B)+(G-E)*(H-F) - s;

  }

};