feature: added 0101 cs

csharp/0101-symmetric-tree.cs

@@ -0,0 +1,36 @@
+/**
+ * Definition for a binary tree node.
+ * public class TreeNode {
+ *     public int val;
+ *     public TreeNode left;
+ *     public TreeNode right;
+ *     public TreeNode(int val=0, TreeNode left=null, TreeNode right=null) {
+ *         this.val = val;
+ *         this.left = left;
+ *         this.right = right;
+ *     }
+ * }
+ */
+public class Solution
+{
+    public bool IsSymmetric(TreeNode root)
+    {
+        return Dfs(root.left, root.right);
+    }
+
+    private bool Dfs(TreeNode leftNode, TreeNode rightNode)
+    {
+        if (leftNode is null || rightNode is null)
+        {
+            return leftNode == rightNode;
+        }
+
+        if (leftNode.val != rightNode.val)
+        {
+            return false;
+        }
+
+        return Dfs(leftNode.left, rightNode.right)
+            && Dfs(leftNode.right, rightNode.left);
+    }
+}