对于三角形来说，重心就是x=(x1+x2+x3)/3，y=(y1+y2+y3)/3
对于多边形
这样
HDU1115
#include<stdio.h> #include<math.h> #include<stdlib.h> struct centre { double x , y ; }; int cas , n ; double Area( centre p0 , centre p1 , centre p2 ) { double area = 0 ; area = p0.x * p1.y + p1.x * p2.y + p2.x * p0.y - p1.x * p0.y - p2.x * p1.y - p0.x * p2.y; return area / 2 ; // 另外在求解的过程中，不需要考虑点的输入顺序是顺时针还是逆时针，相除后就抵消了。 } int main () { centre p0 , p1 , p2 ; double sum_x , sum_y , sum_area , area; scanf ( "%d" , &cas ) ; while ( cas -- ) { sum_x = sum_y = sum_area = 0 ; scanf ( "%d" , &n ) ; scanf ( "%lf%lf" , &p0.x , &p0.y ) ; scanf ( "%lf%lf" , &p1.x , &p1.y ) ; for ( int i = 2 ; i < n ; ++ i ) { scanf ( "%lf%lf" , &p2.x , &p2.y ) ; area = Area(p0,p1,p2) ; sum_area += area ; sum_x += (p0.x + p1.x + p2.x) * area ; sum_y += (p0.y + p1.y + p2.y) * area ; p1 = p2 ; } printf ( "%.2lf %.2lf\n" , sum_x / sum_area / 3 , sum_y / sum_area / 3 ) ; } return 0 ; }
