Merge Two Binary Trees — LeetCode 617 Python Solution

The problem

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.

Example

Input

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

Output

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

Python solution

# 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: Optional[TreeNode], root2: Optional[TreeNode]
    ) -> Optional[TreeNode]:
        if root1 is None:
            return root2
        if root2 is None:
            return root1
        node = TreeNode(root1.val + root2.val)
        node.left = self.mergeTrees(root1.left, root2.left)
        node.right = self.mergeTrees(root1.right, root2.right)
        return node

Complexity

Pattern: Tree Traversal

Choose the order — preorder, inorder, postorder, level — and the problem solves itself. LeetCode 617. Merge Two Binary Trees is filed here because LeetCode tags it Tree and Binary Tree, which is the vocabulary this hub collects.

The tree traversal guide has the Python template for the pattern and the 225 LeetCode problems that use it.

Related problems