/**
knakul853
 */
class Solution {
public:
    vector<vector<int>> levelOrder(TreeNode* root) {

        queue<TreeNode*> q;
        q.push(root);
        vector<vector<int>>ans;

        if( !root ) return ans;

        while( !q.empty() )
        {
            vector<int>res;
            int sz = (int)q.size();
            queue<TreeNode*>temp;

            for( int i=0; i<sz; i++ )
            {
                auto node = q.front();q.pop();
                  res.push_back(node->val);

                if( node->left ) temp.push( node->left );
                if( node->right ) temp.push( node->right );
            }

          q = temp;
            ans.push_back( res );

        }

        return ans;

    }
};