树有几层知道的话可以这样

vector<vector<int> > Print(TreeNode* pRoot) {
    vector<vector<int> > ret;
    if(!pRoot)
        return ret;
    queue<TreeNode*> q;
    q.push(pRoot);
    int cnt = 0;
    int base = 1;
    vector<int> tmp;
    for(int i = 0;i <4096;i ++)
    {
        TreeNode* p = q.front();
        q.pop();
        cnt ++;
        if(p)
            tmp.push_back(p->val);//cout<<p->val<<" ";
        if(cnt==base)
        {
            cnt = 0;
            base = (base<<1);
//            cout<<endl;
            if(tmp.size()!= 0)
            {
                vector<int> t;
                for(int i= 0;i < tmp.size();i ++)
                {
                    t.push_back(tmp[i]);
                }
                ret.push_back(t);
                tmp.clear();
            }
        }
        if(p)
        {
            q.push(p->left);
            q.push(p->right);
        }else
        {
            q.push(NULL);
            q.push(NULL);
        }
    }

    return ret;
}