[코테] 리트코드 트리 617. Merge Two Binary Trees

617. Merge Two Binary Trees

문제 링크

https://leetcode.com/problems/merge-two-binary-trees/description/

문제 설명

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.

제한 사항

• The number of nodes in both trees is in the range [0, 2000].
• -104 <= Node.val <= 10^4

입출력 예 #1

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

입출력 예 #2

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

문제 풀이

재귀 탐색을 통해 두 개의 트리에서 동일 위치에 노드가 있을 경우네는 두 노드의 값을 합한다.

재귀 탐색을 통해서 진행하기에 마지막 순회한 노드인 루트 노드가 리턴된다.

class Solution:
    def mergeTrees(self, root1: Optional[TreeNode], root2: Optional[TreeNode]) -> Optional[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