levelOrder.cpp

class Solution {
public:
    vector<vector<int>> levelOrder(Node* root) 
	  {
     if (!root) 
      return vector<vector<int>>(); 
      vector<vector<int>> res; 
      queue<Node*> q;
      q.push(root);
      while (!q.empty())
      {
          int size = q.size(); 
          vector<int> curLevel;
          for (int i = 0; i < size; i++)
          {
              Node* tmp = q.front();
              q.pop();
              curLevel.push_back(tmp -> val);
              for (Node* n : tmp -> children) 
                   q.push(n); 
          }
          res.push_back(curLevel);
      }
      return res; 
    }
};