code: private Node getParent(Node n) {
          if (n.y_s == null) {
              return null;
          }
          Node c = n.y_s;
          if (c.o_c == n) {
              return c;
          }
          Node p1 = c.y_s;
          if (p1 != null && p1.o_c == n) {
              return p1;
          }
          return c;
      }
docs: /*
  Get the parent node of a given node.