Subject: https://leetcode-cn.com/problems/binary-tree-level-order-traversal-ii/
Answer: Recursive Binary Tree
List<List<Integer>> lists;
public List<List<Integer>> levelOrderBottom(TreeNode root) {
lists = new ArrayList<>();
level(root, 0);
List<List<Integer>> results = new ArrayList<>();
for(int i=0;i<lists.size();i++){
results.add(0,lists.get(i));
}
return results;
}
public void level(TreeNode root, int n){
if(root!=null){
if(n<lists.size()){
lists.get(n).add(root.val);
}else{
List<Integer> list = new ArrayList<>();
list.add(root.val);
lists.add(list);
}
level(root.left,n+1);
level(root.right,n+1);
}
}