POJ-1385 Lifting the Stone 计算几何 多边形重心

POJ-1385 Lifting the Stone

题意： 计算多边形的重心。
分析： 通过计算其中三角形的加权重心得到整个多边形的重心。POJ(g++ wa, c++ ac)很迷。
代码：

#include <cstdio>
#include <algorithm>
#include <cstring>
#include <iostream>
#include <cmath>using namespace std;const int MAXN = 1e6 + 7;
struct Point
{
    long long x, y;Point () {
    }Point (long long _x, long long _y){
    x = _x;y = _y;}Point operator - (const Point b) const {
    return Point (x - b.x, y - b.y);}long long operator ^ (const Point b) const {
    return x * b.y - y * b.x;}Point operator + (const Point b) const {
    return Point (x + b.x, y + b.y);}
};Point p[MAXN];
int n;int main ()
{
    int t;scanf ("%d", &t);while (t--){
    scanf ("%d", &n);for (int i = 0; i < n; i++){
    scanf ("%lld%lld", &p[i].x, &p[i].y);}Point ans (0, 0);long long s = 0; for (int i = 0; i < n; i++){
    long long ss = p[i]^p[(i + 1)%n];s += ss;Point tmp = p[i] + p[(i + 1)%n];ans.x += tmp.x * ss;ans.y += tmp.y * ss;}printf ("%.2lf %.2lf\n", 1.0*ans.x/(3l*s), 1.0*ans.y/(3l*s));}return 0;
}