建立两个递增有序单向链表，合并为一个递增有序链表

以下是两种建立两个递增有序单向链表并合并为一个递增有序链表的方法：

1. 递归方法：

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

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

# 创建链表1
list1 = ListNode(1)
list1.next = ListNode(3)
list1.next.next = ListNode(5)

# 创建链表2
list2 = ListNode(2)
list2.next = ListNode(4)
list2.next.next = ListNode(6)

# 合并链表
merged_list = mergeTwoLists(list1, list2)

# 打印合并后的链表
while merged_list:
    print(merged_list.val)
    merged_list = merged_list.next

2. 迭代方法：

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

def mergeTwoLists(l1, l2):
    dummy = ListNode(0)
    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 or l2
    return dummy.next

# 创建链表1
list1 = ListNode(1)
list1.next = ListNode(3)
list1.next.next = ListNode(5)

# 创建链表2
list2 = ListNode(2)
list2.next = ListNode(4)
list2.next.next = ListNode(6)

# 合并链表
merged_list = mergeTwoLists(list1, list2)

# 打印合并后的链表
while merged_list:
    print(merged_list.val)
    merged_list = merged_list.next