## 题目

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

**Note:**

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.

Example:

1 | Input: |

## 思路

Recursive.

## 代码

1 | # # Definition for a binary tree node. |