Given a constant K and a singly linked list L, you are supposed to reverse the links of every K elements on L. For example, given L being 1→2→3→4→5→6, if K=3, then you must output 3→2→1→6→5→4; if K=4, you must output 4→3→2→1→5→6.
Photoinduced Bending Behaviour of Cross-linked Liquid Crystalline Polymers with High Cross-linking Densities，蒋臻，吕久安，In this paper, highly crosslinked liquid-crystalline polymer (CLCP) films with a longer spacer and different locations and concentrati
方法1
思路：将链表中的元素都保存list中，并判断这个list和反转后的list，是否相同，如果相同，则回文；否则，则不回文。
性能分析：时间复杂度为O(n);空间复杂度为O(n) [因为用到了extra space list]
方法2
思路：将链表等分为两部分，判断前半部分和后半部分的逆序是否相等，如果相等，则回文，否则不回文。
性能分析：时间复杂度为O(n)；空间复杂度为O(1)[no extra space
# Definition for singly-li
