若|x1﹣x2|≥|y1﹣y2|,则点P1(x1 , y1)与点P2(x2 , y2)的“友好距离”为|x1﹣x2|;
若|x1﹣x2|<|y1﹣y2|,则P1(x1 , y1)与点P2(x2 , y2)的“友好距离”为|y1﹣y2|;