此题的巧妙之处在于题目数据非常大只能在原链表中解决，遇到进一的问题如果尽早判断就不会有问题，而且第一位的判断非常巧妙

struct ListNode* doubleIt(struct ListNode* head){
  struct ListNode* Node = (struct ListNode*)malloc(sizeof(struct ListNode));
  struct ListNode* cur = head;
  if (head->val > 4) {
      Node->val = 1;
      Node->next = head;
      head = Node;
      cur = head->next;
  }
  while (cur != NULL) {
      cur->val = cur->val*2%10;
      if (cur->next && cur->next->val > 4) 
          cur->val++;
      cur = cur->next;
  }
  return head;
}