35. 翻转链表

Description

Reverse a linked list.

Example

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

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

public class Solution {
    /**
     * @param head: n
     * @return: The new head of reversed linked list.
     */
    public ListNode reverse(ListNode head) {
        // write your code here
        //Need three pointers
        if (head== null || head.next==null){
            return head;
        } 
        ListNode prev = null;
        ListNode curt = head;
        
        while(curt != null){
            ListNode temp =  curt.next;
            curt.next = prev;
            prev = curt;
            curt = temp;
        }
            
        return prev; 
    }
}

public class Solution {
    /**
     * @param head: n
     * @return: The new head of reversed linked list.
     */
    public ListNode reverse(ListNode head) {
        // write your code here

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

描述
翻转一个链表

您在真实的面试中是否遇到过这个题？  
样例
给出一个链表1->2->3->null，这个翻转后的链表为3->2->1->null

挑战
在原地一次翻转完成