【leetcode】21. 合并两个有序链表

class Solution:
    def mergeTwoLists(self, l1, l2):
        """
        :type l1: ListNode
        :type l2: ListNode
        :rtype: ListNode
        """
        head = ListNode(0)
        first = head
        while l1 is not None and l2 is not None:
            if l1.val <= l2.val:
                head.next = l1
                l1 = l1.next
            else:
                head.next = l2
                l2 = l2.next
            head = head.next
        if l1 is not None:
            head.next = l1
        if l2 is not None:
            head.next = l2
        return first.next