合并两个有序链表

class ListNode:
    def __init__(self, val=0, next=None):
        self.val = val
        self.next = next

def solve():
    def mergeTwoLists(l1, l2):
        if not l1:
            return l2
        if not l2:
            return l1
        if l1.val < l2.val:
            l1.next = mergeTwoLists(l1.next, l2)
            return l1
        else:
            l2.next = mergeTwoLists(l1, l2.next)
            return l2
    l1 = ListNode(1, ListNode(2, ListNode(4)))
    l2 = ListNode(1, ListNode(3, ListNode(4)))
    result = mergeTwoLists(l1, l2)
    vals = []
    while result:
        vals.append(result.val)
        result = result.next
    print(vals)