[222] Count Complete Tree Nodes(TBD)

賺題數？！用recursive 寫法居然這麼簡單？！（大驚）

但是題目說 : Design an algorithm that runs in less than O(n) time complexity.

這邊完全不瞭要如何達成 XD

晚上跟室友求救一下, 先貼個pass版本

/**

* Definition for a binary tree node.

* struct TreeNode {

* int val;

* struct TreeNode *left;

* struct TreeNode *right;

* };

*/

int countNodes(struct TreeNode* root){

if (root == NULL)

return 0;

return 1+countNodes(root->left)+countNodes(root->right);

}