Update 0106.添加C#版

problems/0106.从中序与后序遍历序列构造二叉树.md

@@ -1228,6 +1228,19 @@ impl Solution {
     }
 }
 ```
+### C#
+```C#
+public TreeNode BuildTree(int[] inorder, int[] postorder)
+{
+    if (inorder.Length == 0 || postorder.Length == null) return null;
+    int rootValue = postorder.Last();
+    TreeNode root = new TreeNode(rootValue);
+    int delimiterIndex = Array.IndexOf(inorder, rootValue);
+    root.left = BuildTree(inorder.Take(delimiterIndex).ToArray(), postorder.Take(delimiterIndex).ToArray());
+    root.right = BuildTree(inorder.Skip(delimiterIndex + 1).ToArray(), postorder.Skip(delimiterIndex).Take(inorder.Length - delimiterIndex - 1).ToArray());
+    return root;
+}
+```
 
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