# [leetcode] Count Complete Tree Nodes

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.

if countLeft == countRight, return count(countLeft)

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

```/**
* 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 == nullptr) return 0;
int left = countLeftLevel(root);
int right = countRightLevel(root);
if(left == right){
return count(left);
}
else{
return countNodes(root->left) + countNodes(root->right) + 1;
}
}
int countLeftLevel(TreeNode* root){
int count = -1;
while(root){
count++;
root = root->left;
}
return count;
}
int countRightLevel(TreeNode* root){
int count = -1;
while(root){
count++;
root = root->right;
}
return count;
}
int count(int n){
int sum = 1;
int factor = 2;
while(n--){
sum += factor;
factor *= 2;
}
return sum;
}
};```

This site uses Akismet to reduce spam. Learn how your comment data is processed.