剑指Offer：反转链表

来源：互联网发布：2017理财软件排行编辑：程序博客网时间：2024/04/30 12:59

方法一：

简单粗暴，还有点小问题。只是改了节点的值，没有真正交换2个节点

/*public class ListNode {    int val;    ListNode next = null;    ListNode(int val) {        this.val = val;    }}*/public class Solution {    public ListNode ReverseList(ListNode head) {int len = getLength(head);        ListNode a = head;        ListNode b = null;        int n = 0;        for(int i=1,j=len-1;i<j;i++,j--){            b = getByIndex(head,j);            n = b.val;            b.val = a.val;            a.val = n;                        a = a.next;        }        return head;    }    public int getLength(ListNode head)    {        if( head == null ) return 0;        ListNode a = head;        int len = 1 ;        while(a != null){a = a.next;            len++;        }        return len;    }        public ListNode getByIndex(ListNode head, int x){        if( x <= 0 || head ==null) return null;        ListNode a = head;        int length =1;        while(a != null)        {            if( x == length ){                return a;            }            a = a.next;            length++;        }        return null;    }}

方法2

看了一些别人的代码后发现了这种方法，觉得确实很好。就实现了一遍。

public class Solution {    public ListNode ReverseList(ListNode head) {        if(head == null) return null;                ListNode next = null;        ListNode pre = null;        while(head != null)        {            next = head.next;           head.next = pre;            pre = head;            head = next;        }        return pre;    }}

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