/**
 * Definition for binary tree
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public List<List<Integer>> levelOrderBottom(TreeNode root) {
        ArrayList<List<Integer>> result = new ArrayList<List<Integer>>();
        ArrayList<TreeNode> row = new ArrayList<TreeNode>();
        ArrayList<Integer> rowVals = new ArrayList<Integer>();
        if(root==null)
            return result;

        row.add(root);
        while(!row.isEmpty()){
            rowVals.clear();
            for(int i = 0; i < row.size(); i++){
                TreeNode curr = row.get(i);
                rowVals.add(curr.val);
            }
            result.add(0,(ArrayList<Integer>)rowVals.clone());
            row = traverseRow(row);
        }

        return result;
    }

    public ArrayList<TreeNode> traverseRow(ArrayList<TreeNode> row){
        ArrayList<TreeNode> r = new ArrayList<TreeNode>();
        for(int i = 0; i < row.size(); i++){
            TreeNode curr = row.get(i);
            if(curr.left!=null) r.add(curr.left);
            if(curr.right!=null) r.add(curr.right);
        }

        return r;
    }

}