leetcode 【 Merge Two Sorted Lists 】 python 实现

题目：

Merge two sorted linked lists and return it as a new list. The new list should be made by splicing together the nodes of the first two lists.

代码：oj在线测试通过 Runtime: 208 ms

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

 class Solution:
     # @param two ListNodes
     # @return a ListNode
     def mergeTwoLists(self, l1, l2):
         if l1 is None:
             return l2
         if l2 is None:
             return l1

         dummyhead = ListNode(0)
         dummyhead.next = None
         p = dummyhead
         while l1 is not None and l2 is not None:
             if l1.val > l2.val:
                 p.next = l2
                 l2 = l2.next
             else:
                 p.next = l1
                 l1 = l1.next
             p = p.next
         if l1 is not None:
             p.next = l1
         else:
             p.next = l2
         return dummyhead.next

思路：

虚表头dummyhead设定好了就不要动，设定一个p=hummyhead，然后从处理p.next开始；最后返回hummyhead就可以获得正确的结果

两个表的指针一步步移动，并通过比较val的大小决定哪个插入p.next

注意，每次执行完判断，要移动指针p=p.next