学步园

题目描述：

已经顺序给出多边形的各个顶点，求重心

#include <iostream><br /> #include <algorithm><br /> #include <cmath><br /> using namespace std;</p> <p>struct point{<br /> int x, y;<br /> };</p> <p>point p[1000001];</p> <p>double cal(int i, int j)<br /> {<br /> double res;</p> <p> res = p[i].x*p[j].y - p[j].x*p[i].y;<br /> return res;<br /> }</p> <p>int main()<br /> {<br /> int T, N;<br /> double cx, cy;</p> <p> scanf("%d", &T);<br /> for (int t = 0; t < T; t++)<br /> {<br /> scanf("%d", &N);<br /> for (int i = 0; i < N; i++)<br /> scanf("%d %d", &p[i].x, &p[i].y);<br /> p[N].x = p[0].x;<br /> p[N].y = p[0].y;</p> <p> double A = 0;<br /> for (i = 0; i < N; i++)<br /> {<br /> A += cal(i, i+1);<br /> }<br /> A /= 2;</p> <p> cx = cy = 0;<br /> for (i = 0; i < N; i++)<br /> {<br /> cx += (p[i].x + p[i+1].x)*cal(i, i+1);<br /> cy += (p[i].y + p[i+1].y)*cal(i, i+1);<br /> }<br /> cx /= 6*A;<br /> cy /= 6*A;</p> <p> printf("%.2lf %.2lf/n", cx, cy);<br /> }<br /> return 0;<br /> }