leetcode 206. Reverse Linked List

标签：code   测试   tno   down   val   reverse   分析   linked   转移   

题目内容

Reverse a singly linked list.

Example:

Input: 1->2->3->4->5->NULL
Output: 5->4->3->2->1->NULL
Follow up:

A linked list can be reversed either iteratively or recursively. Could you implement both?

分析过程

• 题目归类：

• 题目分析：

• 边界分析：
  • 空值分析
  • 循环边界分析
• 方法分析：
  • 数据结构分析
  • 状态机
  • 状态转移方程
    
  • 最优解

• 测试用例构建

代码实现

非递归

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
class Solution {
    public ListNode reverseList(ListNode head) {
        ListNode prev = null;
        while(head != null){
            ListNode tmp = head.next;
            head.next = prev;
            prev = head;
            head = tmp;
        }
        return prev;
    }
}

递归

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
class Solution {
    public ListNode reverseList(ListNode head) {
        if(head == null || head.next == null)
            return head;
        ListNode tmp = reverseList(head.next);
        head.next.next = head;
        head.next = null;
        return tmp;
    }
}

效率提高

拓展问题

Reverse Linked List II
Medium
Binary Tree Upside Down
Medium
Palindrome Linked List
Easy

leetcode 206. Reverse Linked List

标签：code   测试   tno   down   val   reverse   分析   linked   转移   

原文地址：https://www.cnblogs.com/clnsx/p/12307742.html