Leetcode 617. Merge Two Binary Trees

개발 초보자·2021년 10월 31일
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문제

You are given two binary trees root1 and root2.

Imagine that when you put one of them to cover the other, some nodes of the two trees are overlapped while the others are not. You need to merge the two trees into a new binary tree. The merge rule is that if two nodes overlap, then sum node values up as the new value of the merged node. Otherwise, the NOT null node will be used as the node of the new tree.

Return the merged tree.

Note: The merging process must start from the root nodes of both trees.



Example 1:

Input: root1 = [1,3,2,5], root2 = [2,1,3,null,4,null,7]

Output: [3,4,5,5,4,null,7]

Example 2:

Input: root1 = [1], root2 = [1,2]

Output: [2,2]

해설

새로운 Treenode를 하나 만들어 root1과 root2의 합을 더해 val에 대입한다. 만일 한쪽이 null인 경우 else 문에 걸려 root1, root2 둘 중에 존재하는 것이 return 된다.

# 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 root1 and root2:
            node = TreeNode(root1.val + root2.val)
            node.left = self.mergeTrees(root1.left, root2.left)
            node.right = self.mergeTrees(root1.right, root2.right)
            return node
        else:
            return root1 or root2 # 둘 중 존재하는 것을 리턴
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