remove method

bool remove(dynamic val)

If there is such a node, remove it

Return false when there is no such node

Implementation

bool remove(val) {
  if (_map.containsKey(val)) {
    final node = _map[val]!;
    for (var from in node.from) {
      from.to.remove(node);
    }
    for (var to in node.to.keys) {
      to.from.remove(node);
    }
    _node_to_val.remove(node);
    _map.remove(val);
    return true;
  }
  return false;
}