题解 | #反转链表#

/*
public class ListNode {
    int val;
    ListNode next = null;

    ListNode(int val) {
        this.val = val;
    }
}*/

public class Solution {

    private int count = 0;

    public ListNode ReverseList(ListNode head) {
        return head == null ? null : reverse(head, head.next);
    }

    private ListNode reverse(ListNode prev, ListNode curr) {
        if (prev == null) return null;
        if (count == 0) prev.next = null;
        count++;
        if (curr != null) {
            ListNode realNext = curr.next;
            curr.next = prev;
            return reverse(curr, realNext);
        } else {
            return prev;
        }
    }
}