Untitled

public class Solution {

    /*
    A
   / | \
   B C  D
        /\
       E  F

Display a node if:
1) it has been selected
2) it is an ancestor of a selected node
3) it shares the same parent as a selected node
     */

    interface Node {
        int getLevel();
        Optional<Node> getParent();
        List<Node> getChildren();
        List<Node> getAncestors();
    }

    // Called frequently
    public Iterable<Node> getDisplayed() throws Exception {
        throw new UnsupportedOperationException("Implement me");
    }

    void handleAddSelection(Node node) {
        throw new UnsupportedOperationException("Implement me");
    }

    void handleRemoveSelection(Node node) {
        throw new UnsupportedOperationException("Implement me");
    }
}