Reverse Second Half of Linked List

package ReverseSecondHalfList;

/**
 * Created by yang on 1/17/17.
 */
class ListNode {
    int val;
    ListNode next;

    ListNode(int x) {
        this.val = x;
    }
}

public class Solution {
    public static ListNode reverseSecondHalfList(ListNode head) {
        if (head == null || head.next == null) {
            return head;
        }

        ListNode slow = head;
        ListNode fast = head;
        while (fast.next != null && fast.next.next != null) {
            slow = slow.next;
            fast = fast.next.next;
        }

        ListNode pre = slow.next;
        ListNode cur = pre.next;
        while (cur != null) {
            pre.next = cur.next;
            cur.next = slow.next;
            slow.next = cur;
            cur = pre.next;
        }

        return head;
    }
}