Binary_Tree_Level_Order_Traversal_II.java

public class Solution {
        public List<List<Integer>> levelOrderBottom(TreeNode root) {
            List<List<Integer>> wrapList = new LinkedList<List<Integer>>();
            levelMaker(wrapList, root, 0);
            return wrapList;
        }

        public void levelMaker(List<List<Integer>> list, TreeNode root, int level) {
            if(root == null) return;
            if(level >= list.size()) {
                list.add(0, new LinkedList<Integer>());
            }
            levelMaker(list, root.left, level+1);
            levelMaker(list, root.right, level+1);
            list.get(list.size()-level-1).add(root.val);
        }
    }