package question;

/**
 * @author Roderland
 * @since 1.0
 */
public class Question206 {
 public ListNode reverseList(ListNode head) {
 ListNode pre = null;
 ListNode cur = head;
 while (cur!=null) {
 ListNode next = cur.next;
 cur.next = pre;
 pre = cur;
 cur = next;
 }
 return pre;
 }

 // 递归
 ListNode res;
 public ListNode reverseList2(ListNode head) {
 if (head==null) return null;
 f(head, null);
 return res;
 }

 public void f(ListNode head, ListNode pre) {
 ListNode next = head.next;
 head.next = pre;
 if (next==null) {
 res = head;
 } else {
 f(next, head);
 }
 }
}