LeetCode-Count Complete Tree Nodes

Given a complete binary tree, count the number of nodes.

Definition of a complete binary tree from Wikipedia:
In a complete binary tree every level, except possibly the last, is completely filled, and all nodes in the last level are as far left as possible. It can have between 1 and 2^h nodes inclusive at the last level h.

Solution:

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public int countNodes(TreeNode root) {
        if (root == null) return 0;
        return countNodesRecur(root);
    }

    public int getLeftHeight(TreeNode cur){
        int h = 1;
        while (cur.left!=null){
            cur = cur.left;
            h++;
        }
        return h;
    }

    public int countNodesRecur(TreeNode root){
        int h = getLeftHeight(root);
        if (h==1) return 1;

        if (root.right==null) return 2;
        int rh = getLeftHeight(root.right);

        if (rh==h-1){
            // root.left is a complete tree with height h-1
            return (1 << rh) -1 + 1 + countNodesRecur(root.right);
        } else {
            // root.right is a complete tree with height h-2
            return (1 << rh) - 1 + 1 + countNodesRecur(root.left);
        }
    }
}