import java.util.List; import java.util.ArrayList; /**  A tree in which each node has an arbitrary number of children.  */ public class Tree { private Node root; class Node { public Object data; public List children; /**  Computes the number of leaves of the subtree whose root is this node.  @return the number of leaves in the subtree  */  public int leafCount() { // ******************************************** // FINISH THIS METHOD // ******************************************** } /**  Computes the size of the subtree whose root is this node.  @return the number of nodes in the subtree  */  public int size() { int sum = 0; for (Node child : children) { sum = sum + child.size(); } return 1 + sum; } } /**  Constructs an empty tree.  */  public Tree() { root = null; } /**  Constructs a tree with one node and no children.  @param rootData the data for the root  */  public Tree(Object rootData) { root = new Node(); root.data = rootData; root.children = new ArrayList(); } /**  Adds a subtree as the last child of the root.  */  public void addSubtree(Tree subtree) { root.children.add(subtree.root); } /**  Counts the number of leaves in the tree  @return the number of leaves in the tree  */  public int leafCount() { if (root == null) { return 0; } else { return root.leafCount(); } } /**  Computes the size of this tree.  @return the number of nodes in the tree  */  public int size() { if (root == null) { return 0; } else { return root.size(); } } }