107. Binary Tree Level Order Traversal II (java)

Author: bluesword12350

solution/0107.Binary Tree Level Order Traversal II/Solution.java

@@ -0,0 +1,23 @@
+class Solution {
+    List<List<Integer>> lists;
+    public List<List<Integer>> levelOrderBottom(TreeNode root) {
+        lists = new ArrayList<>();
+        levelOrderBottom(root,0);
+        List<List<Integer>> result = new ArrayList<>();
+        for (int i = lists.size() - 1; i >= 0; i--) result.add(lists.get(i));
+        return result;
+    }
+    private void levelOrderBottom(TreeNode root, int i) {
+        if (root==null) return;
+        List<Integer> list;
+        if (i==lists.size()){
+            list = new ArrayList<>();
+            lists.add(list);
+        }else {
+            list = lists.get(i);
+        }
+        list.add(root.val);
+        levelOrderBottom(root.left,i+1);
+        levelOrderBottom(root.right,i+1);
+    }
+}