/**

 * Definition for a binary tree node.

 * struct TreeNode {

 *     int val;

 *     TreeNode *left;

 *     TreeNode *right;

 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}

 * };

 */

class Solution {

public:

    vector<vector<int>> levelOrderBottom(TreeNode* root) {

        if(!root) return {};

        queue<TreeNode*> q;

        q.push(root);

        vector<vector<int> > vec;

        while(!q.empty()){

            vector<int> v;;

            for(int i = q.size(); i > ; i--){

                auto t = q.front();

                q.pop();

                v.push_back(t->val);

                if(t->left) q.push(t->left);

                if(t->right) q.push(t->right);

            }

            vec.push_back(v);

        }

        reverse(vec.begin(),vec.end());

        return vec;

    }

};