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/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
      public List<List<Integer>> levelOrderBottom(TreeNode root) {
	LinkedList<List<Integer>> list = new LinkedList<List<Integer>>();
	addLevel(list, 0, root);
	return list;
}

private void addLevel(LinkedList<List<Integer>> list, int level, TreeNode node) {
	if (node == null) return;
	if (list.size()-1 < level) list.addFirst(new LinkedList<Integer>());
	list.get(list.size()-1-level).add(node.val);
	addLevel(list, level+1, node.left);
	addLevel(list, level+1, node.right);
}
        
    
}

# class TreeNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution(object):
    def levelOrderBottom(self, root):
        """
        :type root: TreeNode
        :rtype: List[List[int]]
        """
        res = [];
        if not root:
            return res;
        
        res.append([root.val]);
        frontier1 = [root];
        while(len(frontier1) != 0):
            frontier2 = [];
            temp = [];
            for i in frontier1: #######Explore all the node at current level
                v = i;
                if v.left:
                    frontier2.append(v.left);
                    temp.append(v.left.val);
                if v.right:
                    frontier2.append(v.right);
                    temp.append(v.right.val);
            if temp:
                res.append(temp);
            frontier1 = frontier2;
            
        
        return res[::-1]; ###reverse the result list
        

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public List<List<Integer>> levelOrderBottom(TreeNode root) {
        List<List<Integer>> res = new LinkedList<List<Integer>>();
        if (root == null) return res;
        Queue<TreeNode> queue = new LinkedList<TreeNode>();
        queue.offer(root);
        while (!queue.isEmpty()) {
            int curLen = queue.size();
            List<Integer> level = new LinkedList<Integer>();
            for(int i = 0; i < curLen; i++) {
                TreeNode temp = queue.poll();
                level.add(temp.val);
                if(temp.left != null) queue.offer(temp.left);
                if(temp.right != null) queue.offer(temp.right);
            }
            res.add(0, level);
        }
        return res;
    }
    
}