jzoffer-15:反转链表

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package com.fjf.test;

import com.fjf.test.Test03.ListNode;

/**
*
* 反转链表
* @author fjf
* 2018年8月19日 16:06:51
* 输入一个链表，反转链表后，输出新链表的表头。
*
*/
public class Test15 {

public static void main(String[] args) {
    Mylink l = new Mylink();
    for (int i = 0; i < 7; i++) {
        l.addLink(i);
    }
    System.out.println("链表反转前：" );
    l.print(l.head);

    System.out.println("------------" );    

    Solution s = new Solution();
    ListNode newhead = s.ReverseList(l.head);

    System.out.println("链表反转后：" );
    l.print(newhead);

}



static class Solution{
     public ListNode ReverseList(ListNode head) {
              if(head==null){
                  return null;
              }

              ListNode pre = null;
              ListNode next = null;

              while(head!=null){
                  next = head.next;
                  head.next = pre;

                   pre=head;
                   head = next;
              }
              return pre;
        }
}



  //定义链表
    static class Mylink{
         public ListNode head;
         public ListNode current;


         public void addLink(int data){
             if(head==null){
                 head = new ListNode(data);
                 current = head;
             }else{
                 current.next = new ListNode(data);
                 current = current.next;
             }
         }

         public void print(ListNode head){
                if(head == null){
                    return;
                }

                current = head;
                while(current!=null){
                    System.out.println(current.val);
                    current = current.next;
                }
            } 

    }



     //定义节点
static  class ListNode {
        int val;
        ListNode next = null;

        ListNode(int val) {
            this.val = val;
        }
    }

}

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