[LintCode] 35 Reverse Linked List 解题报告

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



思路
设一个prev和一个next的ListNode。每次把head.next指向prev，并且更新prev和head。


Code

/**
 * 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) {
        // write your code here
        
        ListNode prev = null;
        
        while (head != null) {
            ListNode next = head.next;
            head.next = prev;
            prev = head;
            head = next;
        }
        
        return prev;
    }
}