Update111.二叉树的最小深度，添加C#版

problems/0111.二叉树的最小深度.md

@@ -708,6 +708,49 @@ impl Solution {
     }
 }
 ```
+### C#
+```C#
+// 递归
+public int MinDepth(TreeNode root)
+{
+    if (root == null) return 0;
+    int left = MinDepth(root.left);
+    int right = MinDepth(root.right);
+    if (root.left == null && root.right != null)
+        return 1+right;
+    else if(root.left!=null && root.right == null)
+        return 1+left;
+        
+    int res = 1 + Math.Min(left, right);
+    return res;
+}
+```
+```C#
+// 迭代
+public int MinDepth(TreeNode root)
+{
+    if (root == null) return 0;
+    int depth = 0;
+    var que = new Queue<TreeNode>();
+    que.Enqueue(root);
+    while (que.Count > 0)
+    {
+        int size = que.Count;
+        depth++;
+        for (int i = 0; i < size; i++)
+        {
+            var node = que.Dequeue();
+            if (node.left != null)
+                que.Enqueue(node.left);
+            if (node.right != null)
+                que.Enqueue(node.right);
+            if (node.left == null && node.right == null)
+                return depth;
+        }
+    }
+    return depth;
+}     
+```
 
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