Description
给了一个链表，删除其中重复的节点
My Answer
我的思路很简单 存下before和current的节点，进行比较 记得判断边界case，head是null的情况
Complexity
我自己的解法时间复杂度应该是O(n)了，但是结果却是：
Runtime: 1 ms, faster than 15.21% of Java online submissions for Remove Duplicates from Sorted List. Memory Usage: 41.4 MB, less than 6.06% of Java online submissions for Remove Duplicates from Sorted List.
Other Answer
- 可以优化成为只要一个辅助节点。优化过后是：
Runtime: 0 ms, faster than 100.00% of Java online submissions for Remove Duplicates from Sorted List. Memory Usage: 38.6 MB, less than 35.44% of Java online submissions for Remove Duplicates from Sorted List.>
- 可以用递归