https://leetcode.cn/problems/merge-two-binary-trees/ (opens new window) 需要注意的点

• 前序遍历

# 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:

        if not root1:
            return root2
        if not root2:
            return root1
        
        merge = TreeNode(root1.val+root2.val)
        merge.left = self.mergeTrees(root1.left, root2.left)
        merge.right = self.mergeTrees(root1.right, root2.right)
        return merge