[leetcode]206.Reverse Linked List

標籤：class   rev   儲存   next   list   linked   代碼   can   def   

題目

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?

解法一思路

鏈表逆轉題，鏈表題在表頭加一個頭結點會比較好。第一種方法用非遞迴的方法，每次用tmp來儲存要移動前面的結點，然後先刪除tmp結點，然後把tmp結點插入到頭結點後面即可。

代碼

/** * 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) return head;        ListNode fakehead = new ListNode(0);        fakehead.next = head;        while(head.next != null) {            ListNode tmp = head.next;            head.next = tmp.next;            tmp.next = fakehead.next;            fakehead.next = tmp;        }        return fakehead.next;    }}

解法二思路

用遞迴的方法寫.

代碼

/** * 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 newhead = reverseList(head.next);                head.next.next = head;        head.next = null;        return newhead;    }}

[leetcode]206.Reverse Linked List