leetcode.222. 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 countNodes(TreeNode* root) {
if(root==NULL) return 0;

int l = getLeft(root) ;
int r = getRight(root) ;

if(l==r) {
return (2<<l) - 1;
} else {
return countNodes(root->left) + countNodes(root->right) + 1;
}
}
int getLeft(TreeNode* root) {
int count = 0;
while(root->left!=NULL) {
root = root->left;
++count;
}
return count;
}

int getRight(TreeNode* root) {
int count = 0;
while(root->right!=NULL) {
root = root->right;
++count;
}
return count;
}
};