【高斯消元】BZOJ1013 [JSOI2008]球形空间产生器sphere

题面在这里

高斯消元裸题，把球心的坐标设出来，再搞一搞把二次项消掉就好了

示例程序：

#include<cstdio>#include<algorithm>#define _abs(x) ((x)>0?(x):-(x))using namespace std;const int maxn=15;const double eps=1e-5;int n;double x[maxn][maxn],a[maxn][maxn],ans[maxn];int fcmp(double x){    if (_abs(x)<=eps) return 0;    return x>0?1:-1;}void Gauss(int n){    for (int i=1;i<=n;i++){        int where=-1;        for (int j=i;j<=n;j++)         if (fcmp(a[j][i]-0)!=0) {where=j;break;}        swap(a[where],a[i]);        //if where<0 无解        for (int j=i+1;j<=n;j++){            double w=a[j][i]/a[i][i];            for (int k=i;k<=n+1;k++) a[j][k]-=a[i][k]*w;        }    }    for (int i=n;i>=1;i--){        ans[i]=a[i][n+1]/a[i][i];        for (int j=1;j<i;j++) a[j][n+1]-=ans[i]*a[j][i];    }}int main(){    scanf("%d",&n);    for (int i=1;i<=n+1;i++)     for (int j=1;j<=n;j++) scanf("%lf",&x[i][j]);    for (int i=2;i<=n+1;i++)     for (int j=1;j<=n;j++) a[i-1][j]=2*(x[1][j]-x[i][j]),a[i-1][n+1]+=x[1][j]*x[1][j]-x[i][j]*x[i][j];    Gauss(n);    for (int i=1;i<n;i++) printf("%.3lf ",ans[i]);printf("%.3lf",ans[n]);    return 0;}