From b83cc1602a91c6d9ad3268904d17be42415d6938 Mon Sep 17 00:00:00 2001
From: ironartisan <54694467+ironartisan@users.noreply.github.com>
Date: Sun, 5 Sep 2021 10:27:23 +0800
Subject: [PATCH] =?UTF-8?q?=E6=B7=BB=E5=8A=A00404.=E5=B7=A6=E5=8F=B6?=
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---
 problems/0404.左叶子之和.md | 26 +++++++++++++++++++++++++-
 1 file changed, 25 insertions(+), 1 deletion(-)

diff --git a/problems/0404.左叶子之和.md b/problems/0404.左叶子之和.md
index 2b627b6c..c0eb7c8e 100644
--- a/problems/0404.左叶子之和.md
+++ b/problems/0404.左叶子之和.md
@@ -201,7 +201,31 @@ class Solution {
     }
 }
 ```
-
+```java
+// 层序遍历迭代法
+class Solution {
+    public int sumOfLeftLeaves(TreeNode root) {
+        int sum = 0;
+        if (root == null) return 0;
+        Queue<TreeNode> queue = new LinkedList<>();
+        queue.offer(root);
+        while (!queue.isEmpty()) {
+            int size = queue.size();
+            while (size -- > 0) {
+                TreeNode node = queue.poll();
+                if (node.left != null) { // 左节点不为空
+                    queue.offer(node.left);
+                    if (node.left.left == null && node.left.right == null){ // 左叶子节点
+                        sum += node.left.val;
+                    }
+                }
+                if (node.right != null) queue.offer(node.right);
+            }
+        }
+        return sum;
+    }
+}
+```
 
 
 ## Python