【LeetCode刷题】206 反转链表 java

【LeetCode刷题】206 反转链表 java 2023-01-05 420

题目

给你单链表的头节点 head ，请你反转链表，并返回反转后的链表。

示例

方法一：迭代

比如需要链表为 1->2->3->4->null ，反转后就是null <--1 <-- 2 <-- 3 <-- 4

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

方法二：递归

class Solution {
    public ListNode reverseList(ListNode head) {
        if (head == null || head.next == null) {
            return head;
        }
        ListNode p = reverseList(head.next);
        head.next.next = head;
        head.next = null;
        return p;
    }
}