92. Reverse Linked List II

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.

Solution

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
public class Solution {
    public ListNode reverseBetween(ListNode head, int m, int n) {
              ListNode dummyNode = new ListNode(-1);
        dummyNode.next = head;

        ListNode prev = dummyNode;
        for(int i = 1; i < m; i ++) {
            prev = prev.next;
        }

        ListNode cur = prev.next;
        ListNode speical = cur;
        if (cur.next == null) {
            return dummyNode.next;
        } else {
            cur = cur.next;
        }

        for(int i = m; i < n; i ++) {
            ListNode temp = cur.next;

            ListNode prevNext = prev.next;
            prev.next = cur;
            cur.next = prevNext;

            speical.next = temp;
            cur = temp;
        }

        return dummyNode.next;
    }
}