【算法】Rectangles' Area

int solution(int K, int L, int M, int N, int P, int Q, int R, int S) {
    // write your code in C++11 (g++ 4.8.2)
    int endx    = std::max(M, R);
    int startx  = std::min(K, P);
    int width   = M - K + R - P - (endx-startx);

    int endy    = std::max(N,S);
    int starty  = std::min(L,Q);
    int height  = N - L + S - Q - ( endy - starty );

    return (M - K) * (N - L) + (R - P) * (S - Q) - width * height;
}