Interview Question for Member of Technical Staff at Adobe:

/**
 Returns the max root-to-leaf depth of the tree.
 Uses a recursive helper that recurs down to find
 the max depth.
*/
public int maxDepth() {
  return(maxDepth(root));
}
private int maxDepth(Node node) {
  if (node==null) {
    return(0);
  }
  else {
    int lDepth = maxDepth(node.left);
    int rDepth = maxDepth(node.right);

    // use the larger + 1
    return(Math.max(lDepth, rDepth) + 1);
  }
}