Merge pull request #2096 from jianghongcheng/master

修改py

problems/0111.二叉树的最小深度.md

@@ -302,36 +302,72 @@ class Solution {
 
 ## Python 
 
-递归法：
+递归法（版本一）
 
 ```python
-# 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 minDepth(self, root: TreeNode) -> int:
-        if not root:
+    def getDepth(self, node):
+        if node is None:
             return 0
+        leftDepth = self.getDepth(node.left)  # 左
+        rightDepth = self.getDepth(node.right)  # 右
         
-        if not root.left and not root.right:
-            return 1
+        # 当一个左子树为空，右不为空，这时并不是最低点
+        if node.left is None and node.right is not None:
+            return 1 + rightDepth
         
-        left_depth = float('inf')
-        right_depth = float('inf')
+        # 当一个右子树为空，左不为空，这时并不是最低点
+        if node.left is not None and node.right is None:
+            return 1 + leftDepth
         
-        if root.left:
-            left_depth = self.minDepth(root.left)
-        if root.right:
-            right_depth = self.minDepth(root.right)
-        
-        return 1 + min(left_depth, right_depth)
+        result = 1 + min(leftDepth, rightDepth)
+        return result
+
+    def minDepth(self, root):
+        return self.getDepth(root)
 
 ```
+递归法（版本二）
 
-迭代法：
+```python
+class Solution:
+    def minDepth(self, root):
+        if root is None:
+            return 0
+        if root.left is None and root.right is not None:
+            return 1 + self.minDepth(root.right)
+        if root.left is not None and root.right is None:
+            return 1 + self.minDepth(root.left)
+        return 1 + min(self.minDepth(root.left), self.minDepth(root.right))
+
+
+```
+递归法（版本三）前序
+
+```python
+class Solution:
+    def __init__(self):
+        self.result = float('inf')
+
+    def getDepth(self, node, depth):
+        if node is None:
+            return
+        if node.left is None and node.right is None:
+            self.result = min(self.result, depth)
+        if node.left:
+            self.getDepth(node.left, depth + 1)
+        if node.right:
+            self.getDepth(node.right, depth + 1)
+
+    def minDepth(self, root):
+        if root is None:
+            return 0
+        self.getDepth(root, 1)
+        return self.result
+
+
+```
+迭代法
 
 ```python
 # Definition for a binary tree node.
@@ -364,39 +400,7 @@ class Solution:
         return depth
 ```
 
-迭代法：
 
-```python
-# 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 minDepth(self, root: TreeNode) -> int:
-        if not root:
-            return 0
-        
-        queue = collections.deque([(root, 1)])
-        
-        while queue:
-            node, depth = queue.popleft()
-            
-            # Check if the node is a leaf node
-            if not node.left and not node.right:
-                return depth
-            
-            # Add left and right child to the queue
-            if node.left:
-                queue.append((node.left, depth+1))
-            if node.right:
-                queue.append((node.right, depth+1))
-        
-        return 0
-
-```
 
 ## Go