leetcode206 反转链表 两种做法（循环，递归）

反转链表 leetcode206

方法1 循环

public ListNode reverseList(ListNode head) {
        if (head == null || head.next == null) {
            return head;
        }
        ListNode now = head;
        while (now.next != null) {
            ListNode temp = now.next;
            now.next = now.next.next;
            temp.next = head;
            head = temp;
        }
        return head;
    }

方法2 递归

public ListNode reverseList2(ListNode head) {
        if (head == null || head.next == null) {
            return head;
        }
        ListNode newHead = reverseList2(head.next);
        ListNode now =newHead;
        while (now.next != null) {
            now = now.next;
        }
        now.next = head;
        head.next = null;
        return newHead;
    }