链表_leetcode21

# Definition for singly-linked list.
# class ListNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.next = None

class Solution(object):
    def mergeTwoLists(self, l1, l2):
        """
        :type l1: ListNode
        :type l2: ListNode
        :rtype: ListNode
        """


        cur1 = l1
        cur2 = l2

        dummyHead = ListNode(0)

        pre = dummyHead

        while cur1 and cur2:

            if cur1.val <= cur2.val:
                pre.next = cur1
                pre = pre.next
                cur1 = cur1.next
            else:
                pre.next=cur2
                pre = pre.next
                cur2 = cur2.next


        if  cur1:
            pre.next = cur1

        if cur2:
            pre.next = cur2


        return dummyHead.next