Update 0617.合并二叉树.md

添加 创建 root节点 和 python queue的代码优化版本
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jianghongcheng
2023-05-09 15:11:13 -05:00
committed by GitHub
parent 7eea41ee0e
commit a45046be8a

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@ -352,8 +352,7 @@ class Solution {
```
### Python
**递归法 - 前序遍历**
(版本一) 递归 - 前序 - 修改root1
```python
# Definition for a binary tree node.
# class TreeNode:
@ -377,8 +376,33 @@ class Solution:
return root1 # ⚠️ 注意: 本题我们重复使用了题目给出的节点而不是创建新节点. 节省时间, 空间.
```
(版本二) 递归 - 前序 - 新建root
```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 mergeTrees(self, root1: TreeNode, root2: TreeNode) -> TreeNode:
# 递归终止条件:
# 但凡有一个节点为空, 就立刻返回另外一个. 如果另外一个也为None就直接返回None.
if not root1:
return root2
if not root2:
return root1
# 上面的递归终止条件保证了代码执行到这里root1, root2都非空.
root = TreeNode() # 创建新节点
root.val += root1.val + root2.val# 中
root.left = self.mergeTrees(root1.left, root2.left) #左
root.right = self.mergeTrees(root1.right, root2.right) # 右
return root # ⚠️ 注意: 本题我们创建了新节点.
**迭代法**
```
(版本三) 迭代
```python
class Solution:
def mergeTrees(self, root1: TreeNode, root2: TreeNode) -> TreeNode:
@ -413,7 +437,44 @@ class Solution:
return root1
```
(版本四) 迭代 + 代码优化
```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
from collections import deque
class Solution:
def mergeTrees(self, root1: TreeNode, root2: TreeNode) -> TreeNode:
if not root1:
return root2
if not root2:
return root1
queue = deque()
queue.append((root1, root2))
while queue:
node1, node2 = queue.popleft()
node1.val += node2.val
if node1.left and node2.left:
queue.append((node1.left, node2.left))
elif not node1.left:
node1.left = node2.left
if node1.right and node2.right:
queue.append((node1.right, node2.right))
elif not node1.right:
node1.right = node2.right
return root1
```
### Go
```go