modified the code of 102

Author: Li Li

Algorithms Basics/Chapter 3. Binary Tree/102. Binary Tree Level Order Traversal.cs

@@ -1,7 +1,8 @@
 public class Solution {
     public IList<IList<int>> LevelOrder(TreeNode root) {
+        List<IList<int>> result = new List<IList<int>>();
+        if (root == null) return result;
         Queue<TreeNode> queue = new Queue<TreeNode>();
-        var result = new List<IList<int>>();
         queue.Enqueue(root);            
         while (queue.Count > 0) {
             List<int> level = new List<int>();

Algorithms Basics/Chapter 3. Binary Tree/Binary Tree Traversal (Iteration).cs

@@ -77,9 +77,10 @@ public IList<int> PostorderTraversal(TreeNode root) {
     }
     // level order
     public IList<IList<int>> LevelOrder(TreeNode root) {
+        List<IList<int>> result = new List<IList<int>>();
+        if (root == null) return result;
         Queue<TreeNode> queue = new Queue<TreeNode>();
-        var result = new List<IList<int>>();
-        queue.Enqueue(root);            
+        queue.Enqueue(root);
         while (queue.Count > 0) {
             List<int> level = new List<int>();
             int size = queue.Count;