Reverse Linked List

Reverse Linked List (leetcodelintcode)

Description
Reverse a linked list.

Example
For linked list 1-
>
2-
>
3, the reversed linked list is 3-
>
2-
>
1

Challenge 
Reverse it in-place and in one-pass

解题思路

这里要注意一点，就是尾结点的next是null，利用这一点可以简化操作。

Java 实现

/**
 * Definition for ListNode.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int val) {
 *         this.val = val;
 *         this.next = null;
 *     }
 * }
 */
public
class
Solution
{

/**
     * 
@param
 head: The head of linked list.
     * 
@return
: The new head of reversed linked list.
     */
public
 ListNode 
reverse
(ListNode head)
{

if
 (head == 
null
 || head.next == 
null
) {

return
 head;
        }

        ListNode prev = 
null
;

while
 (head != 
null
) {
            ListNode temp = head.next;
            head.next = prev;
            prev = head;
            head = temp;
        }


return
 prev;
    }
}