Update 0513.找树左下角的值.md -添加C#迭代法

Author: Chenxue3

problems/0513.找树左下角的值.md

@@ -716,9 +716,55 @@ public void Traversal(TreeNode root, int depth)
     return;
 }
 ```
+```csharp
+/*
+ * @lc app=leetcode id=513 lang=csharp
+ * 迭代法
+ * [513] Find Bottom Left Tree Value
+ */
+
+// @lc code=start
+public class Solution
+{
+    public int FindBottomLeftValue(TreeNode root)
+    {
+        Queue<TreeNode> que = new Queue<TreeNode>();
+
+        if (root != null)
+        {
+            que.Enqueue(root);
+        }
+        
+        int ans = 0;
+        while (que.Count != 0)
+        {
+           
+            int size = que.Count;
+            for (var i = 0; i < size; i++)
+            {
+                var curNode = que.Peek();
+                que.Dequeue();
+                if(i == 0){
+                    ans = curNode.val;
+                }
+                if (curNode.left != null)
+                {
+                    que.Enqueue(curNode.left);
+                }
+                if (curNode.right != null)
+                {
+                    que.Enqueue(curNode.right);
+                }
+            }
+
+        }
+        return ans;
+    }
+}
+// @lc code=end
+```
 
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