CLRS10.2-7练习 - 翻转单向列表

要求：

Give a Θ(n)-time nonrecursive procedure that reverses a singly linked list of n
elements. The procedure should use no more than constant storage beyond that
needed for the list itself.

中心思想是同时取出并保存链表中的连续三个元素（previous, current, after），并翻转前两个，然后每次将这三个指针依次向后移一位并重复翻转前两个，直至结束

伪代码：

LIST-REVERSE(L)

1 previous = L.head

2 if previous.next ≠ NIL

3　　current = previous.next

4 else return

5 if current.next ≠ NIL

6　　after = current.next

7 else L.head = current

8　　current.next = previous; previous.next = NIL

9　　return

10 current.next = previous; previous.next = NIL

11 while after.next ≠ NIL

12　　previous = current

13　　current = after

14　　after = after.next

15　　current.next = previous

16 after.next = current

17 L.head = after

18 return

存储空间开销-三个指针