222. Count Complete Tree Nodes

Difficulty: Medium

Frequency: N/A

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.

My solution:
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Code:
/**
* 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) {
int cnt = 0, h = height(root);
while (root) {
if (height(root->right) == h - 1) {
cnt += 1 << h;
root = root->right;
} else {
cnt += 1 << h - 1;
root = root->left;
}
h--;
}
return cnt;
}
int height(TreeNode* node) {
return !node ? -1 : 1 + height(node->left);
}
};

Another solution:
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Things to learn: