hdu 1115 Lifting the Stone 多边形的重心

 

  
    

   
     
   
     #include
   
     <
   
     iostream
   
     >
   
     
#include
   
     <
   
     cmath
   
     >
   
     

   
     using
   
      
   
     namespace
   
      std;

   
     struct
   
      point{
 
   
     double
   
      x,y;
 point (
   
     double
   
      xx
   
     =
   
     0
   
     ,
   
     double
   
      yy
   
     =
   
     0
   
     ){
 x
   
     =
   
     xx; y
   
     =
   
     yy;
 }
 
   
     double
   
      
   
     operator
   
      
   
     *
   
     (point b){
 
   
     return
   
      x
   
     *
   
     b.y
   
     -
   
     y
   
     *
   
     b.x;
 }
}p[
   
     1000001
   
     ];

   
     int
   
      main()
{
 
   
     int
   
      T,N,i;
 scanf(
   
     "
   
     %d
   
     "
   
     ,
   
     &
   
     T);
 
   
     while
   
     (T
   
     --
   
     )
 {
 scanf(
   
     "
   
     %d
   
     "
   
     ,
   
     &
   
     N);
 
   
     for
   
     (i
   
     =
   
     0
   
     ;i
   
     <
   
     N;i
   
     ++
   
     )
 scanf(
   
     "
   
     %lf%lf
   
     "
   
     ,
   
     &
   
     p[i].x,
   
     &
   
     p[i].y);
 p[N].x
   
     =
   
     p[
   
     0
   
     ].x; p[N].y
   
     =
   
     p[
   
     0
   
     ].y; 
 
   
     double
   
      area
   
     =
   
     0
   
     ;
 point re;
 
   
     for
   
     (i
   
     =
   
     0
   
     ;i
   
     <
   
     N;i
   
     ++
   
     )
 {
 area
   
     +=
   
     p[i]
   
     *
   
     p[i
   
     +
   
     1
   
     ];
 re.x
   
     +=
   
     (p[i].x 
   
     +
   
      p[i
   
     +
   
     1
   
     ].x)
   
     *
   
      (p[i]
   
     *
   
     p[i
   
     +
   
     1
   
     ]);
 re.y
   
     +=
   
     (p[i].y 
   
     +
   
      p[i
   
     +
   
     1
   
     ].y)
   
     *
   
      (p[i]
   
     *
   
     p[i
   
     +
   
     1
   
     ]);
 }
 area
   
     /=
   
     2
   
     ;
 re.x 
   
     /=
   
      
   
     6
   
     *
   
     area;
 re.y 
   
     /=
   
      
   
     6
   
     *
   
     area;
 printf(
   
     "
   
     %.2lf %.2lf\n
   
     "
   
     ,re.x,re.y);
 }
 
   
     return
   
      
   
     0
   
     ;
}