Merge two sorted linked lists and return it as a new list. The new list should be made by splicing together the nodes of the first two lists.

Example:

Input: 1->2->4, 1->3->4Output: 1->1->2->3->4->4

# Definition for singly-linked list.# class ListNode(object):#     def __init__(self, x):#         self.val = x#         self.next = Noneclass Solution(object):    def mergeTwoLists(self, l1, l2):        """        :type l1: ListNode        :type l2: ListNode        :rtype: ListNode        """        if not l1 and l2:            return l2        if not l2 and l1:            return l1        if not l1 and not l2:            return []                it1=l1        it2=l2        if it1.val<=it2.val:            node=ListNode(it1.val)            it1=it1.next        else:            node=ListNode(it2.val)            it2=it2.next        ll=node        while it1 and it2:            if it1.val<=it2.val:                node1=ListNode(it1.val)                it1=it1.next                node.next=node1                node=node1            else:                node1=ListNode(it2.val)                node.next=node1                node=node1                it2=it2.next                    if it1:            node.next=it1        elif it2:            node.next=it2        return ll