Merge pull request #535 from KelvinG-611/513.找树左下角的值

更新 513.找树左下角的值 python部分代码

problems/0513.找树左下角的值.md

@@ -274,27 +274,51 @@ class Solution {
 
 
 Python：
+
+**递归 - 回溯**
 ```python
-//递归法
-# Definition for a binary tree node.
-# class TreeNode:
-#     def __init__(self, val=0, left=None, right=None):
-#         self.val = val
-#         self.left = left
-#         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")
+        leftmost_val = 0
+
+        def __traverse(root, cur_depth): 
+            nonlocal max_depth, leftmost_val
+            if not root.left and not root.right: 
+                if cur_depth > max_depth: 
+                    max_depth = cur_depth
+                    leftmost_val = root.val  
+            if root.left: 
+                cur_depth += 1
+                __traverse(root.left, cur_depth)
+                cur_depth -= 1
+            if root.right: 
+                cur_depth += 1
+                __traverse(root.right, cur_depth)
+                cur_depth -= 1
+
+        __traverse(root, 0)
+        return leftmost_val
+```
+**迭代 - 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：