[LC 92.反转链表2]

递归解法

/**
 * 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 {
    ListNode successor = null;
    public ListNode reverseBetween(ListNode head, int left, int right) {

        if (left == 1){
            return reverseN(head,right);
        }
        head.next = reverseBetween(head.next,left-1,right-1);
        return head;
    }

    public ListNode reverseN(ListNode head,int n){
            if(n == 1){
                successor = head.next;
                return head;
            }
            ListNode last = reverseN(head.next,n-1);
            head.next.next = head;
            head.next = successor;
            return last;
        }
}