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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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@ -352,8 +352,7 @@ class Solution {
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```
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### Python
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**递归法 - 前序遍历**
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(版本一) 递归 - 前序 - 修改root1
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```python
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# Definition for a binary tree node.
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# class TreeNode:
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@ -377,8 +376,33 @@ class Solution:
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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.
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```
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(版本二) 递归 - 前序 - 新建root
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```python
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# Definition for a binary tree node.
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# class TreeNode:
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# def __init__(self, val=0, left=None, right=None):
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# self.val = val
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# self.left = left
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# self.right = right
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class Solution:
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def mergeTrees(self, root1: TreeNode, root2: TreeNode) -> TreeNode:
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# 递归终止条件:
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# 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.
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if not root1:
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return root2
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if not root2:
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return root1
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# 上面的递归终止条件保证了代码执行到这里root1, root2都非空.
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root = TreeNode() # 创建新节点
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root.val += root1.val + root2.val# 中
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root.left = self.mergeTrees(root1.left, root2.left) #左
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root.right = self.mergeTrees(root1.right, root2.right) # 右
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return root # ⚠️ 注意: 本题我们创建了新节点.
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**迭代法**
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```
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(版本三) 迭代
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```python
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class Solution:
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def mergeTrees(self, root1: TreeNode, root2: TreeNode) -> TreeNode:
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@ -413,7 +437,44 @@ class Solution:
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return root1
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```
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(版本四) 迭代 + 代码优化
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```python
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# Definition for a binary tree node.
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# class TreeNode:
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# def __init__(self, val=0, left=None, right=None):
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# self.val = val
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# self.left = left
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# self.right = right
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from collections import deque
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class Solution:
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def mergeTrees(self, root1: TreeNode, root2: TreeNode) -> TreeNode:
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if not root1:
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return root2
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if not root2:
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return root1
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queue = deque()
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queue.append((root1, root2))
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while queue:
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node1, node2 = queue.popleft()
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node1.val += node2.val
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if node1.left and node2.left:
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queue.append((node1.left, node2.left))
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elif not node1.left:
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node1.left = node2.left
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if node1.right and node2.right:
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queue.append((node1.right, node2.right))
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elif not node1.right:
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node1.right = node2.right
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return root1
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```
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### Go
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```go
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