From 2f412e5c7d3b41b66946d92e699330cb7e5e5036 Mon Sep 17 00:00:00 2001
From: Kelvin <guanli611@outlook.com>
Date: Thu, 29 Jul 2021 11:18:26 -0400
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1. 更改python 递归代码: 上一版本python代码跟卡哥思路不一样, 感觉把不同的解题方法放在这里不方便初学者学习. 所以建议更改.
2. 添加迭代方法代码.
---
 problems/0513.找树左下角的值.md | 61 +++++++++++++++++++++-----
 1 file changed, 49 insertions(+), 12 deletions(-)

diff --git a/problems/0513.找树左下角的值.md b/problems/0513.找树左下角的值.md
index 17d15fde..391118ab 100644
--- a/problems/0513.找树左下角的值.md
+++ b/problems/0513.找树左下角的值.md
@@ -274,8 +274,9 @@ class Solution {
 
 
 Python：
+
+**递归法 - 回溯**
 ```python
-//递归法
 # Definition for a binary tree node.
 # class TreeNode:
 #     def __init__(self, val=0, left=None, right=None):
@@ -284,17 +285,53 @@ Python：
 #         self.right = right
 class Solution:
     def findBottomLeftValue(self, root: TreeNode) -> int:
-        depth=0
-        self.res=[]
-        def level(root,depth):
-            if not root:return
-            if depth==len(self.res):
-                self.res.append([])
-                self.res[depth].append(root.val)
-            level(root.left,depth+1)
-            level(root.right,depth+1)
-        level(root,depth)
-        return self.res[-1][0]
+        max_depth = -float("INF")
+        max_left_value = -float("INF")
+
+        def __traversal(root, left_len): 
+            nonlocal max_depth, max_left_value
+
+            if not root.left and not root.right: 
+                if left_len > max_depth: 
+                    max_depth = left_len
+                    max_left_value = root.val
+                return 
+
+            if root.left: 
+                left_len += 1
+                __traversal(root.left, left_len)
+                left_len -= 1
+
+            if root.right: 
+                left_len += 1
+                __traversal(root.right, left_len)
+                left_len -= 1
+            return 
+        
+        __traversal(root, 0)
+
+        return max_left_value
+```
+
+**迭代法 - 层序遍历**
+```python
+class Solution:
+    def findBottomLeftValue(self, root: TreeNode) -> int:
+        queue = deque()
+        if root: 
+            queue.append(root)
+        result = 0
+        while queue: 
+            q_len = len(queue)
+            for i in range(q_len): 
+                if i == 0: 
+                    result = queue[i].val 
+                cur = queue.popleft()
+                if cur.left: 
+                    queue.append(cur.left)
+                if cur.right: 
+                    queue.append(cur.right)
+        return result
 ```
 Go：