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

Definition of a complete binary tree from :

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 2hnodes inclusive at the last level h.

1 /** 2  * Definition for a binary tree node. 3  * struct TreeNode { 4  *     int val; 5  *     TreeNode *left; 6  *     TreeNode *right; 7  *     TreeNode(int x) : val(x), left(NULL), right(NULL) {} 8  * }; 9  */10 class Solution {11 public:12     int countNodes(TreeNode* root) {13         if(root==NULL)14             return 0;15         TreeNode* tmp=root->left;16         int leftheight=1;17         int rightheight=1;18         while(tmp!=NULL)19         {20             tmp=tmp->left;21             leftheight++;22         }23         tmp=root->right;24          while(tmp!=NULL)25         {26             tmp=tmp->right;27             rightheight++;28         }29         if(leftheight==rightheight)30         {31             return (1<
     
      left)+countNodes(root->right)+1;35     }36 };