new_contents: # -*- coding:utf-8 -*-
  # 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 not l1:
              return l2
          if not l2:
              return l1
  
          head = None
          if l1.val > l2.val:
              head = l2
              l2 = l2.next
          else:
              head = l1
              l1 = l1.next
          index = head
          while l1 and l2:
              if l1.val > l2.val:
                  index.next = l2
                  l2 = l2.next
              else:
                  index.next = l1
                  l1 = l1.next
              index = index.next
          if l1:
              index.next = l1
          elif l2:
              index.next = l2
          return head
  
subject: add leetcode Merge Two Sorted Lists