LeetCode 617 - 合并二叉树

class Solution:
    def mergeTrees(self, root1: Optional[TreeNode], root2: Optional[TreeNode]) -> Optional[TreeNode]:
        if root1 is None and root2 is None:
            return None
        root = TreeNode(0)
        if root1 and root2:
            root.val = root1.val + root2.val
        elif root1 and not root2:
            root.val = root1.val
        elif not root1 and root2:
            root.val = root2.val

        # 如果结点本身没有子树了就直接传入空
        root.left = self.mergeTrees(root1.left if root1 else None, root2.left if root2 else None)
        root.right = self.mergeTrees(root1.right if root1 else None, root2.right if root2 else None)
        return root