今天面试某FAANG厂被问了一道多叉树的题非递归

大致意思是这样的，没答好
Considering a N-ary tree with this node structure:

class NodeTypeA {
  String payload;
  List<NodeTypeA> children;
}
And we want to convert the tree to NodeTypeB tree, but the internal structure of NodeTypeB is invisible, and we can only construct the new tree using two method:

//This method can only convert leaf NodeTypeA (no children)
public NodeTypeB convertLeaf(NodeTypeA nodeTypeA);
//This method can convert a non-leaf NodeTypeA as long as its children are converted
public NodeTypeB convertParent(NodeTypeA parentNodeTypeA, List<NodeTypeB> nodeTypeBs);

The recursive solution is trivial, how can we do it in non-recursive way?