Find the total area covered by two?rectilinear?rectangles in a?2Dplane.
Each rectangle is defined by its bottom left corner and top right corner as shown in the figure.

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

求兩個矩形的總面積， 關(guān)鍵點在于求矩形是否相交， 以及交集的面積。

判斷是否相交： 1的左x點和2的右x點， 1 的右x點和2的左x點， 1的下y點和2的上y點， 1的上y點和2的下y點比較。