Reverse Linked List II

1. Title

Reverse Linked List II

2.   Http address

https://leetcode.com/problems/reverse-linked-list-ii/

3. The question

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.

4. My code(AC)

    //  Accepted
    public ListNode reverseBetween(ListNode head, int m, int n) {
         
        ListNode frontDump = new ListNode(-1);
        ListNode middleDump = new ListNode(-1);
        ListNode lastDump = new ListNode(-1);
        ListNode frontTail = frontDump;
        ListNode middleTail = null;
        ListNode tmp = null;
        int len = 1;
        frontDump.next = head;
        ListNode p = head;
        
        while( p != null &&  len < m)
        {
            frontTail = p;
            p = p.next;
            len++;
        }
        frontTail.next = null;
        
        middleDump.next = p;
        middleTail = p;
        while( p != null && len <= n)
        {
            tmp = p.next;
            p.next = middleDump.next;
            middleDump.next = p;
            p = tmp;
            len++;
        }
        
        lastDump.next = p;
        
        if( m == 1)
        {
            middleTail.next = lastDump.next;
            return middleDump.next;
        }
        if( middleDump.next != null)
        {
            frontTail.next = middleDump.next;
            middleTail.next = lastDump.next;
        }else{
            frontTail.next = lastDump.next;
        }
        return frontDump.next;
    }