/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
public:
    int height = 0;
    void countHeight(TreeNode* root) {
        if (!root) return;
        else {
            height += 1;
            countHeight(root->left);
        }
    }
    TreeNode* findNode(TreeNode* root, int num) {
        TreeNode* temp = root;
        for (int i = height; i > 0; i--) {
            if (temp && (num & (1 << (i - 1)))) {
                temp = temp->right;
            } else if (temp) temp = temp->left;
        }
        return temp;
    }
    int countNodes(TreeNode* root) {
        if (!root) return 0;
        countHeight(root->left);
        if (height == 0) return 1;
        int right = pow(2, height) - 1, left = 0, mid = (left + right) / 2;
        while (left < right) {
            if (findNode(root, mid)) {
                left = mid + 1;
            } else right = mid - 1;
            mid = (left + right) / 2;
        }
        if (findNode(root, left))
            return pow(2, height) + left;
        else
            return pow(2, height) - 1 + left;
    }
};