class Solution {
public:
    vector<vector<int>> levelOrder(TreeNode* root) {
         vector<vector<int>> v2;
         
        if(!root) return v2;
        vector<vector<int>> v1;
        queue<TreeNode *>q1;
        q1.push(root);
        while(!q1.empty()){
             vector<int> v;
            int sz=q1.size();
            while(sz--){
                //vector<int> v;
                TreeNode *cur = q1.front();
                q1.pop();
                if(cur->left) q1.push(cur->left);
                if(cur->right)q1.push(cur->right);
                
                v.push_back(cur->val);
                //v1.push_back(v);
              
            }
             v1.push_back(v);

        }

        return v1;
    }
};