class ListNode:

def init(self, x):self.val = xself.next = Noneclass Solution:def mergeTwoLists(self, l1, l2):""":type l1: ListNode:type l2: ListNode:rtype: ListNode"""

head = ListNode(0)    first = head    while l1!=None and l2!=None:        if l1.val <= l2.val:            head.next = l1            l1 = l1.next        else:            head.next = l2            l2 = l2.next        head = head.next    if l1 != None:        head.next = l1    elif l2 != None:        head.next = l2    return first.next

head1 = ListNode(1)

n1 = ListNode(2)n2 = ListNode(4)n3 = ListNode(5)head1.next = n1n1.next = n2n2.next = n3

有序链表

head2 = ListNode(1)

m1 = ListNode(2)m2 = ListNode(3)m3 = ListNode(8)head2.next = m1m1.next = m2m2.next = m3

s = Solution()

res = s.mergeTwoLists(head1,head2)while res:print(res.val)res = res.next