单链表翻转-需要默写过的三种方法

1. 直接翻转

class Solution {
    public ListNode reverseList(ListNode head) {
        ListNode prev = null;
        ListNode curr = head;
        
        while (curr != null) {
            ListNode next = curr.next;
            curr.next = prev;
            prev = curr;
            curr = next;
        }
        return prev;
    }
}

2. 头插法
	ListNode reverseList(ListNode head) { //左闭右开区间
        ListNode dummy = new ListNode(-1);
        ListNode cur = head;
        while (cur != null) {
            ListNode next = cur.next;
            cur.next = dummy.next;
            dummy.next = cur;
            cur = next;
        }
        return dummy.next;
    }
 
3. 递归