typedef double T;
struct triple {
int i, j, k;
triple() {}
triple(int i, int j, int k) : i(i), j(j), k(k) {}
};
vector<triple> delaunayTriangulation(vector<T>& x, vector<T>& y) {
int n = x.size();
vector<T> z(n);
vector<triple> ret;
for (int i = 0; i < n; i++)
z[i] = x[i] * x[i] + y[i] * y[i];
for (int i = 0; i < n-2; i++) {
for (int j = i+1; j < n; j++) {
for (int k = i+1; k < n; k++) {
if (j == k) continue;
double xn = (y[j]-y[i])*(z[k]-z[i]) - (y[k]-y[i])*(z[j]-z[i]);
double yn = (x[k]-x[i])*(z[j]-z[i]) - (x[j]-x[i])*(z[k]-z[i]);
double zn = (x[j]-x[i])*(y[k]-y[i]) - (x[k]-x[i])*(y[j]-y[i]);
bool flag = zn < 0;
for (int m = 0; flag && m < n; m++)
flag = flag && ((x[m]-x[i])*xn +
(y[m]-y[i])*yn +
(z[m]-z[i])*zn <= 0);
if (flag) ret.push_back(triple(i, j, k));
}
}
}
return ret;
}