Will the Guru

/**
 * 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) {
        ListNode dummy = new ListNode();
        dummy.next = head;
        
        ListNode before = dummy;
        for (int i=1;i<left;i++) {
            before = before.next;
        }
        
        ListNode prev = before;
        ListNode curr = before.next;

        ListNode nextNode = null;
        for (int i=left;i<=right;i++) {
            nextNode = curr.next;
            curr.next = prev;
            prev = curr;
            curr = nextNode;
        }

        before.next.next = curr;
        before.next = prev;

        return dummy.next;
    }
}

ListNode reverseList(ListNode head) {
    ListNode prev = null;
    ListNode curr = head;
    while (curr != null) {
        ListNode nextNode = curr.next; // first, make sure we don't lose the next node
        curr.next = prev;              // reverse the direction of the pointer
        prev = curr;                   // set the current node to prev for the next node
        curr = nextNode;               // move on
    }

    return prev;
}