https://leetcode.com/problems/count-complete-tree-nodes

count-complete-tree-nodes.cpp

class Solution {
public:
    int countNodes(TreeNode* root) {
        if (root == nullptr) return 0;
        int left_height = 0;
        int right_height = 0;
        for (auto temp = root; temp != nullptr; temp = temp->left) left_height += 1;
        for (auto temp = root; temp != nullptr; temp = temp->right) right_height += 1;
        if (left_height == right_height) return pow(2, left_height) - 1;
        return 1 + countNodes(root->left) + countNodes(root->right);
    }
};