606. Construct String from Binary Tree

https://leetcode.com/problems/construct-string-from-binary-tree/

Python

Recursion

class Solution:
    def tree2str(self, root: Optional[TreeNode]) -> str:

        def preorder(node, result):
            if not node:
                return

            result.append(str(node.val))

            if node.left:
                result.append('(')
                preorder(node.left, result)
                result.append(')')
            else:
                if node.right:
                    result.append('()')
            if node.right:
                result.append('(')
                preorder(node.right, result)
                result.append(')')

        result = []
        preorder(root, result)
        return ''.join(result)