class Solution {
public:
    vector<vector<int>> levelOrder(TreeNode* root) {
        if(root==NULL){
            return {};
        }
        queue<TreeNode*> q;
        q.push(root);
        vector<vector<int>> v;
        v.push_back({root->val});
        while(q.size()!=0){
            int n = q.size();
            vector<int> s;
            for(int i=0; i<n; i++){
                if(q.front()->left!=NULL){
                    q.push(q.front()->left);
                    s.push_back(q.front()->left->val);
                }
                if(q.front()->right!=NULL){
                    q.push(q.front()->right);
                    s.push_back(q.front()->right->val);
                }
                q.pop();
            }
            v.push_back(s);
        }
        v.erase(v.end()-1);
        return v;

    }
};