合并两个有序链表

def solve():
    class ListNode:
        def __init__(____):
            self.val = val
            self.next = next
    
    # 创建链表1: ____->____->____
    l1 = ListNode(____)
    l1.next = ListNode(____)
    l1.next.next = ListNode(____)
    
    # 创建链表2: ____->____->____
    l2 = ListNode(____)
    l2.next = ListNode(____)
    l2.next.next = ListNode(____)
    
    dummy = ListNode(____)
    curr = dummy
    while l1 and l2:
        if l1.val <= l2.val:
            curr.next = l1
            l1 = l1.next
        else:
            curr.next = l2
            l2 = l2.next
        curr = curr.next
    curr.next = l1 if l1 else l2
    
    result = []
    node = dummy.next
    while node:
        result.append(str(____))
        node = node.next
    print('____'.join(____))