Reverse Linked List II

/**
 * Definition for ListNode
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) {
 *         val = x;
 *         next = null;
 *     }
 * }
 */
public class Solution {
    /**
     * @param ListNode head is the head of the linked list 
     * @oaram m and n
     * @return: The head of the reversed ListNode
     */
    public ListNode reverseBetween(ListNode head, int m , int n) {
        if(head == null  || m > n){
            return head;
        }
        ListNode dummy =  new ListNode(1);
        dummy.next = head;
        head = dummy;
        
        for(int i = 1 ; i < m; i++){
            head = head.next;
        }
        
        ListNode prev = head;
        ListNode curr = head.next;
        ListNode Nnode = curr;
        ListNode next = curr.next;
        
        for(int i = m; i< n; i++){
            ListNode temp = next.next;
            next.next = curr;
            curr = next;
            next = temp;
        }
        Nnode.next = next;
        prev.next = curr;
        return dummy.next;
    }
}