Method add_point

code/geometry/rmst.cpp:15–16

  int n;
  RMST() : n(0) {}
  void add_point(int x, int y) {
    arr[arr[n].i = n].x = x, arr[n++].y = y; }
  void rec(int l, int r) {
    if (l >= r) return;
    int m = (l+r)/2;