Reverse Linked List II. Leetcode 92.

ReverseLinkedListII.java

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode() {}
 *     ListNode(int val) { this.val = val; }
 *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
 * }
 */
class Solution {
    public ListNode reverseBetween(ListNode head, int left, int right) {
        int count = 1;
        ListNode prev = null;
        ListNode curr = head;
        while (count < left) {
            prev = curr;
            curr = curr.next;
            count++;
        }
        ListNode beforeSublist = prev;
        ListNode lastOfSublist = curr;
        while (count <= right) {
            ListNode nextNode = curr.next;
            curr.next = prev;
            prev = curr;
            curr = nextNode;
            count++;
        }
        if (beforeSublist != null) {
            beforeSublist.next = prev;
        } else {
            head = prev;
        }
        lastOfSublist.next = curr;
        return head;
    }
}