/**
* Retrieves nodes from root to leaf and returns leaf index.
*
* @param feat feature vector
* @param root_id starting root index
* @return leaf index
*/
public int getLeafIndex(FVec feat, int root_id) {
int pid = root_id;
while (!nodes[pid].is_leaf()) {
int split_index = nodes[pid].split_index();
pid = getNext(pid, feat.fvalue(split_index));
}
return pid;
}