001矩形面积

class Solution {
public:
    int computeArea(int ax1, int ay1, int ax2, int ay2, int bx1, int by1, int bx2, int by2) {
      int s1 = (ax2-ax1)*(ay2-ay1);
      int s2 = (bx2 - bx1)*(by2 - by1);
      //定重叠的上下左右位置。
      int overw = min(ax2,bx2) - max(ax1,bx1);
      int overh = min(ay2,by2) - max(ay1,by1);
     //int overarea = overh * overw;//错误：如果不重叠则面积为负数，防止负负得正
      int overarea = max(0,overh)*max(0,overw); //不相交就取0
      return s1+s2-overarea;
    }
};