class Solution {
public:
    int countNodes(TreeNode* root) {
        if (!root) return 0;
        auto l = root->left, r = root->right;
        int x = 1, y = 1;
        while (l) l = l->left, x ++ ;
        while (r) r = r->right, y ++ ;
        if (x == y) return (1 << x) - 1;
        return countNodes(root->left) + 1 + countNodes(root->right);
    }
};