92. 反转链表 II

class Solution {
    public ListNode reverseBetween(ListNode head, int m, int n) {
        
        if(m == 1) {
            ListNode node = reverse(head,n);
            return node;
        }
        head.next = reverseBetween(head.next,m-1,n-1);
        return head;
    }
    ListNode last = null;
    public ListNode reverse(ListNode head, int k) {
        
        if(k == 1) {
            last = head.next;
            return head;
        }
        ListNode node = reverse(head.next,k-1);
        head.next.next = head;
        head.next = last;
        return node;
        
    }
}