以最有效的方式合并两个排序的链表

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

def mergeTwoLists(l1, l2):
    dummy = ListNode(0)  # 创建一个虚拟头节点
    curr = dummy  # 指针指向虚拟头节点

    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

    # 将剩余的链表连接到新链表的末尾
    if l1:
        curr.next = l1
    if l2:
        curr.next = l2

    return dummy.next  # 返回新链表的头节点