# Definition for singly-linked list.

# class ListNode:

#     def __init__(self, x):

#         self.val = x

#         self.next = None

class Solution:

    def mergeTwoLists(self, l1: ListNode, l2: ListNode) -> ListNode:

        res = ListNode(None)

        node = res

        while l1 and l2:

            if l1.val<l2.val:

                node.next,l1=l1,l1.next

            else:

                node.next,l2=l2,l2.next

            node = node.next

        if l1:

            node.next=l1

        else:

            node.next=l2

        return res.next

class Solution:

    def mergeTwoLists(self, l1: ListNode, l2: ListNode) -> ListNode:

        if l1 is None and l2 is None:

            return None

        if l1 is None:

            return l2

        if l2 is None:

            return l1

        if l1.val > l2.val:

            l2.next = self.mergeTwoLists(l1, l2.next)

            return l2

        l1.next = self.mergeTwoLists(l1.next, l2)

        return l1