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 2h nodes inclusive at the last level h.
Example:
Input:
1
/ \
2 3
/ \ /
4 5 6
Output: 6输出一颗完全二叉树的结点个数。
这道题其实按照层序遍历一次树，然后把每一层的结点个数相加即可。