count complete tree nodes

# class TreeNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None
class (object):
    def countNodes(self, root):
        """
        :type root: TreeNode
        :rtype: int
        """
        if not root:
            return 0
        left = right = root
        l = r = 0
        while left:
            l += 1
            left = left.left
        while right:
            r += 1
            right = right.right
        if r == l:
            return 2**r -1
        else:
            return self.countNodes(root.left) + self.countNodes(root.right) + 1