[LintCode] Reverse Linked List

Reverse Linked List

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

 

SOLUTION：

这题以前先要对着纸画一遍，后来发现，真的很简单，忘了的话就画一下就行了。思路就是，记录一个pre点，一个curr点，还有一个curr.next点（因为翻转了之后这个点就找不到了，所以要先记录一下）然后 curr.next ---->pre, pre一到当前curr上，curr移到curr.next那个地方就行，不断把curr.next指针指到pre上就ok。

代码：

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