23.cpp

/*

Count Complete Tree Nodes
-------------------------

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

*/

class Solution {
public:
    int countNodes(TreeNode* root) {
        if(root == NULL) return 0;
        return 1 + countNodes(root->left) + countNodes(root->right);
    }
};