P4035 [JSOI2008]球形空间产生器

Link
一道高斯消元的题目，其实重点还是在如何得出方程组也就是增广矩阵。

代码

const double EPS=1e-7;
inline int gauss(double a[][N], bool l[], double ans[], const int& n) {
    int res = 0, r = 0;
    for(int i = 0; i < n; i++)
        l[i] = false;
    for(int i = 0; i < n; i++) {
        for(int j = r; j < n; j++)
            if(fabs(a[j][i]) > EPS) {
                for(int k = i; k <= n; k++)
                    swap(a[j][k], a[r][k]);
                break;
            }
        if(fabs(a[r][i]) < EPS) {
            ++res;
            continue;
        }
        for(int j = 0; j < n; j++)
            if(j != r && fabs(a[j][i]) > EPS) {
                double tmp = a[j][i] / a[r][i];
                for(int k = i; k <= n; k++)
                    a[j][k] -= tmp * a[r][k];
            }
        l[i] = true;
        ++r;
    }
    for(int i = 0; i < n; i++)
        if(l[i])
            for(int j = 0; j < n; j++)
                if(fabs(a[j][i]) > EPS)
                    ans[i] = a[j][n] / a[j][i];
    return res;
}
double b[N][N], a[N][N];
double ans[N];
bool l[N];
int n;
void solve() {
    cin >> n;
    for(int i = 0; i < n + 1; i++) {
        for(int j = 0; j < n; j++) {
            cin >> b[i][j];
        }
    }
    for(int i = 0; i < n; i++) {
        for(int j = 0; j < n; j++)
            a[i][n] += b[i][j] * b[i][j] - b[i+1][j]*b[i+1][j];
    }
    for(int i = 0; i < n; i++) {
        for(int j = 0; j < n; j++) {
            a[i][j] = 2 * (b[i][j] - b[i+1][j]);
        }
    }
    gauss(a, l, ans, n);
    for(int i = 0; i < n; i++)
        printf("%.3lf ", ans[i]);
    cout << endl;
}