Update.二叉树迭代遍历，C#版

problems/二叉树的迭代遍历.md

@@ -695,6 +695,67 @@ impl Solution {
     }
 }
 ```
+### C#
+```C#
+// 前序遍历
+public IList<int> PreorderTraversal(TreeNode root)
+{
+    var st = new Stack<TreeNode>();
+    var res = new List<int>();
+    if (root == null) return res;
+    st.Push(root);
+    while (st.Count != 0)
+    {
+        var node = st.Pop();
+        res.Add(node.val);
+        if (node.right != null)
+            st.Push(node.right);
+        if (node.left != null)
+            st.Push(node.left);
+    }
+    return res;
+}  
+
+// 中序遍历
+public IList<int> InorderTraversal(TreeNode root)
+{
+    var st = new Stack<TreeNode>();
+    var res = new List<int>();
+    var cur = root;
+    while (st.Count != 0 || cur != null)
+    {
+        if (cur != null)
+        {
+            st.Push(cur);
+            cur = cur.left;
+        }
+        else
+        {
+            cur = st.Pop();
+            res.Add(cur.val);
+            cur = cur.right;
+        }
+    }
+    return res;
+}
+// 后序遍历
+public IList<int> PostorderTraversal(TreeNode root)
+{
+    var res = new List<int>();
+    var st = new Stack<TreeNode>();
+    if (root == null) return res;
+    st.Push(root);
+    while (st.Count != 0)
+    {
+        var cur = st.Pop();
+        res.Add(cur.val);
+        if (cur.left != null) st.Push(cur.left);
+        if (cur.right != null) st.Push(cur.right);
+    }
+    res.Reverse(0, res.Count());
+    return res;
+}
+```
 
 <p align="center">
 <a href="https://programmercarl.com/other/kstar.html" target="_blank">