求任意多边形重心（附HDU - 1115 Lifting the Stone代码）

Centre-of-Gravity(Polygon).cpp

@@ -0,0 +1,54 @@
+#include <cstdio>
+
+using namespace std;
+
+struct point
+{
+	double x, y;
+	point(double _x = 0, double _y = 0) : x(_x), y(_y) { }
+}d[1000010];
+
+int t, n;
+
+inline double abs(double x)
+{
+	return x < 0 ? -x : x;
+}
+
+inline point operator - (const point &a, const point &b)
+{
+	return point(a.x - b.x, a.y - b.y);
+}
+
+inline double cross(const point &a, const point &b)
+{
+	return a.x * b.y - a.y * b.x;
+}
+
+inline double area(const point &a, const point &b, const point &c)
+{
+	return cross(b - a, c - a) / 2.0;
+}
+
+int main()
+{
+	scanf("%d", &t);
+	while (t--)
+	{
+		scanf("%d", &n);
+		for (int i = 0; i < n; i++)
+		{
+			scanf("%lf%lf", &d[i].x, &d[i].y);
+		}
+		double sumx = 0, sumy = 0, areasum = 0;
+		for (int i = 2; i < n; i++)
+		{
+			double a = area(d[0], d[i - 1], d[i]);
+			sumx += (d[0].x + d[i - 1].x + d[i].x) / 3.0f * a;
+			sumy += (d[0].y + d[i - 1].y + d[i].y) / 3.0f * a;
+			areasum += a;
+		}
+		printf("%.2lf %.2lf\n", sumx / areasum + 1e-8, sumy / areasum + 1e-8);
+	}
+	return 0;
+}