[leetcode] Count Complete Tree Nodes

From : https://leetcode.com/problems/count-complete-tree-nodes/
Given a complete binary tree, count the number of nodes.

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.

/**
* Definition for a binary tree node.
* struct TreeNode {
*     int val;
*     TreeNode *left;
*     TreeNode *right;
*     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/
class Solution {
public:
int leftLevel(TreeNode* node) {
if(!node) return 0;
int level = 1, num;
while(node->left) {
level++;
node = node->left;
}
return level;
}
int rightLevel(TreeNode* node) {
if(!node) return 0;
int level = 1, num;
while(node->right) {
level++;
node = node->right;
}
return level;
}
int countNodes(TreeNode* root) {
if(!root) return 0;
int ll = leftLevel(root);
int rl = rightLevel(root);
if(ll == rl) return (1<<ll)-1;
return 1 + countNodes(root->left) + countNodes(root->right);

}
};