new_contents: # https://leetcode.com/problems/remove-linked-list-elements/
  from ListNode import ListNode
  class Solution(object):
      def removeElements(self, head, val):
          res = head
          pre = None
          while head :
              if head.val == val :
                  if not pre :
                      res = head.next
                  else:
                      pre.next = head.next
              else:
                  pre = head
              head = head.next
          return res
  
subject: remove linked list elements