Leetcode:Reverse Linked List II 单链表区间范围内逆置

Reverse a linked list from position m to n. Do it in-place and in one-pass.

For example:
Given 1->2->3->4->5->NULL, m = 2 and n = 4,

return 1->4->3->2->5->NULL.

Note:
Given m, n satisfy the following condition:
1 ≤ m ≤ n ≤ length of list.

代码如下：

class Solution {public:    ListNode *reverseBetween(ListNode *head, int m, int n) {        if(head == NULL)            return NULL;        ListNode dummy(0);        dummy.next = head;        ListNode *pre = &dummy;        ListNode *p = head;        int k = 1;                while(k < m)        {            pre = p;            p = p->next;            k++;        }                ListNode *tail = NULL;        ListNode *nxt = NULL;        ListNode *tmp = p;        while(k <= n)        {            nxt = p->next;            p->next = tail;            tail = p;            p = nxt;            k++;        }                pre->next = tail;        tmp->next = p;                return dummy.next;    }};