public class BinaryTreeNode<T> {
  protected T value;
  protected BinaryTreeNode<T> left;
  protected BinaryTreeNode<T> right;

  /**
  * Constructs a BinaryTreeNode with the given value.
  * @param value  A value.
  */
  public BinaryTreeNode(T value) {
    this.value = value;
  }

  /**
  * Get the value.
  */
  public T get() {
    return value;
  }

  /**
  * Gets the left subtree.
  */
  public BinaryTreeNode<T> getLeft() {
    return left;
  }

  /**
  * Gets the right subtree.
  */
  public BinaryTreeNode<T> getRight() {
    return right;
  }

  /**
  * Sets the left subtree.
  * @param t  A tree.
  */
  public void setLeft(BinaryTreeNode<T> t) {
    left = t;
  }

  /**
  * Sets the right subtree.
  * @param t  A tree.
  */
  public void setRight(BinaryTreeNode<T> t) {
    right = t;
  }


  /**
  * Computes the number of nodes in the tree.
  */
  public int size() {
    int l = left != null ? left.size() : 0;
    int r = right != null ? right.size() : 0;
    return 1 + l + r;
  }

  /**
  * Returns a string representation of the tree.
  */
  public String toString() {
    // (v l r)
    if (left == null && right == null) {
      return value.toString();
    }
    String l = left != null ? left.toString() : "<e>";
    String r = right != null ? right.toString() : "<e>";
    return "(" + value.toString() + " " + l + " " + r + ")";
  }

  /**
  * Returns the edge height of the given tree.
  * @param t  A tree or null for the empty tree.
  */
  public static <E> int getHeight(BinaryTreeNode<E> t) {
    if (t == null) {
      return -1;
    }
    int lh = getHeight(t.getLeft());
    int rh = getHeight(t.getRight());
    return lh > rh ? lh + 1 : rh + 1;
  }

}