Leetcode--reverse Linked List II

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.

/** * Definition for singly-linked list. * struct ListNode {*     int val; *     ListNode *next; *     listnode (int x): Val (x), Next (NULL) {} *}; */class Soluti On {public:    listnode *reversebetween (listnode *head, int m, int n)     {        if (head = = NULL | | head->next = NULL || M==n)            return head;        listnode* he = head;        listnode* pre = head;        int i=1;        while (i<m)        {            he = Pre;            Pre = pre->next;            i++;        }        listnode* pre_end = pre;        listnode* end = pre->next;        while (I<n)        {            Pre_end->next = end->next;            End->next = pre;            Pre = end;            End = pre_end->next;            i++;        }        if (m==1)            return pre;        He->next = pre;        return head;    };

Leetcode--reverse Linked List II