Find k-unbalanced Nodes

Find k-unbalanced nodes
EPI Solution
https://github.com/epibook/epibook.github.io/blob/master/solutions/java/src/main/java/com/epi/KBalancedBinaryTreeTemplate.java
  private static <T> Pair<BinaryTree<T>, Integer> findNonKBalancedNodeHelper(
      BinaryTree<T> n, int k) {
    // Empty tree.
    if (n == null) {
      return new Pair<BinaryTree<T>, Integer>(null, 0);
    }

    // Early return if left subtree is not k-balanced.
    Pair<BinaryTree<T>, Integer> L = findNonKBalancedNodeHelper(n.getLeft(), k);
    if (L.getFirst() != null) {
      return L;
    }
    // Early return if right subtree is not k-balanced.
    Pair<BinaryTree<T>, Integer> R = findNonKBalancedNodeHelper(n.getRight(), k);
    if (R.getFirst() != null) {
      return R;
    }

    int nodeNum = L.getSecond() + R.getSecond() + 1; // # of nodes in n.
    if (Math.abs(L.getSecond() - R.getSecond()) > k) {
      return new Pair<BinaryTree<T>, Integer>(n, nodeNum);
    }
    return new Pair<BinaryTree<T>, Integer>(null, nodeNum);
  }

  private static <T> BinaryTree<T> findNonKBalancedNode(BinaryTree<T> n, int k) {
    return findNonKBalancedNodeHelper(n, k).getFirst();
  }