Merge pull request #748 from RyouMon/master

优化 0257.二叉树的所有路径.md Python3解法; 修复 0654.最大二叉树.md Python3解法

problems/0257.二叉树的所有路径.md

@@ -408,25 +408,57 @@ class Solution {
 Python：
 ```Python
 class Solution:
+    """二叉树的所有路径 递归法"""
+
     def binaryTreePaths(self, root: TreeNode) -> List[str]:
-        path=[]
+        path, result = '', []
-        res=[]
+        self.traversal(root, path, result)
-        def backtrace(root, path):
+        return result
-            if not root:return 
+    
-            path.append(root.val)
+    def traversal(self, cur: TreeNode, path: List, result: List):
-            if (not root.left)and (not root.right):
+        path += str(cur.val)
-               res.append(path[:])
+        # 如果当前节点为叶子节点，添加路径到结果中
-            ways=[]
+        if not (cur.left or cur.right):
-            if root.left:ways.append(root.left)
+            result.append(path)
-            if root.right:ways.append(root.right)
+            return
-            for way in ways:
+            
-                backtrace(way,path)
+        if cur.left:
-                path.pop()
+            self.traversal(cur.left, path + '->', result)
-        backtrace(root,path)
+            
-        return ["->".join(list(map(str,i))) for i in res]
+        if cur.right:
+            self.traversal(cur.right, path + '->', result)
 
 ```
 
+```python
+from collections import deque
+
+
+class Solution:
+    """二叉树的所有路径 迭代法"""
+
+    def binaryTreePaths(self, root: TreeNode) -> List[str]:
+        # 题目中节点数至少为1
+        stack, path_st, result = deque([root]), deque(), []
+        path_st.append(str(root.val))
+
+        while stack:
+            cur = stack.pop()
+            path = path_st.pop()
+            # 如果当前节点为叶子节点，添加路径到结果中
+            if not (cur.left or cur.right):
+                result.append(path)
+            if cur.right:
+                stack.append(cur.right)
+                path_st.append(path + '->' + str(cur.right.val))
+            if cur.left:
+                stack.append(cur.left)
+                path_st.append(path + '->' + str(cur.left.val))
+
+        return result
+```
+
+
 Go：
 ```go
 func binaryTreePaths(root *TreeNode) []string {

problems/0654.最大二叉树.md

@@ -258,16 +258,30 @@ class Solution {
 ## Python 
 
 ```python
-//递归法
 class Solution:
+    """最大二叉树 递归法"""
+
     def constructMaximumBinaryTree(self, nums: List[int]) -> TreeNode:
-        if not nums: return None   //终止条件
+        return self.traversal(nums, 0, len(nums))
-        root = TreeNode(max(nums))   //新建节点
+    
-        p = nums.index(root.val)   //找到最大值位置
+    def traversal(self, nums: List[int], begin: int, end: int) -> TreeNode:
-        if p > 0: //保证有左子树
+        # 列表长度为0时返回空节点
-            root.left = self.constructMaximumBinaryTree(nums[:p])   //递归
+        if begin == end:
-        if p < len(nums): //保证有右子树
+            return None
-            root.right = self.constructMaximumBinaryTree(nums[p+1:])  //递归
+        
+        # 找到最大的值和其对应的下标
+        max_index = begin
+        for i in range(begin, end):
+            if nums[i] > nums[max_index]:
+                max_index = i
+        
+        # 构建当前节点
+        root = TreeNode(nums[max_index])
+        
+        # 递归构建左右子树
+        root.left = self.traversal(nums, begin, max_index)
+        root.right = self.traversal(nums, max_index + 1, end)
+        
         return root
 ```