#!/usr/bin/env python3 # -*- coding: utf-8 -*- # author: bt3gl class Node: def __init__(self, val=0, next=None): self.val = val self.next = next def merge_two_list(list1: Optional[Node], list2: Optional[Node]) -> Optional[Node]: if not list1: return list2 if not list2: return list1 if list1.val < list2.val: list1.next = merge_two_list(list1.next, list2) return list1 else: list2.next = merge_two_list(list1, list2.next) return list2