class Solution {
private:
    int simple(TreeLinkNode *root)
    {
        if (root->left == NULL)
            return 1;
        simple(root->left);
        int d = simple(root->right) + 1;
        if (d > 1)
        {
            TreeLinkNode *l = root->left, *r = root->right;
            for(int i = d - 1; i; --i)
            {
                l->next = r;
                l = l->right;
                r = r->left;
            }
        }
        return d;
    }
public:
    void connect(TreeLinkNode *root) {
        if (root == NULL)
            return;
        simple(root);
    }
};