leetcode 之Copy List with Random Pointer（23）

深拷贝一个链表，不同的是这个链表有个额外的随机指针。参考：http://blog.csdn.net/ljiabin/article/details/39054999

做法非常的巧妙，分成三步，一是新建结点，并放在旧结点之后；二是修改新结点的random指针；三是将新旧链表断开。

RandomListNode *randomList(RandomListNode *head)
      {
          //复制每个结点，并将新结点放在旧结点之后
          for (RandomListNode *cur = head; cur != nullptr;)
          {
              RandomListNode *node = new RandomListNode(cur->label);
              node->next = cur->next;
              cur->next = node;
              cur = node->next;
          }

          //修改新结点的Random指针
          for (RandomListNode *cur = head; cur != nullptr;)
          {
              if (cur->random != nullptr)cur->next->random = cur->random->next;

              cur = cur->next->next;
          }

          //将新旧链表断开
          RandomListNode dummy(-1);
          for (RandomListNode *cur = head,*new_cur=&dummy; cur != nullptr;)
          {
              new_cur->next = cur->next;
              new_cur = new_cur->next;

              cur->next = cur->next->next;
              cur = cur->next;

          }

          return dummy.next;
      }