用python写出：有两个带附加头结点的单链表，结点包含两个域：entry和next，若单链表中的元素值递增有序排列，请写算法，将两个单链表按顺序合并成一个链表。

class Node:
    def __init__(self, entry=None, next=None):
        self.entry = entry
        self.next = next
        
class LinkedList:
    def __init__(self):
        self.head = Node()
        
    def add(self, entry):
        new_node = Node(entry)
        current = self.head
        while current.next and current.next.entry < entry:
            current = current.next
        new_node.next = current.next
        current.next = new_node
        
    def merge(self, other):
        current1 = self.head.next
        current2 = other.head.next
        merged_list = LinkedList()
        while current1 and current2:
            if current1.entry < current2.entry:
                merged_list.add(current1.entry)
                current1 = current1.next
            else:
                merged_list.add(current2.entry)
                current2 = current2.next
        while current1:
            merged_list.add(current1.entry)
            current1 = current1.next
        while current2:
            merged_list.add(current2.entry)
            current2 = current2.next
        return merged_list

使用方法：

list1 = LinkedList()
list1.add(1)
list1.add(3)
list1.add(5)

list2 = LinkedList()
list2.add(2)
list2.add(4)
list2.add(6)

merged_list = list1.merge(list2)
current = merged_list.head.next
while current:
    print(current.entry)
    current = current.next

输出结果：

1
2
3
4
5
6