最常见的程序员面试题(1)单链表反向

一个单链表如何反向? 在不增加额外链表对象的情况下。仔细的分析这个题目可以知道: 一个N长度的链表反向需要N次循环，也就是每次循环要改变一个next指针的值。同时，为了让循环能继续，当前的cur->next指针要保存下来，作为下次运行的cur指针。在用一个指针来保存反向后，新的next指针要指向的位置。

    分别用C++和Java来实现。

[cpp] view plaincopyprint?

1. #include "stdafx.h"   
2. struct node{  
3.     int data;  
4.     node* pNext;  
5.     explicit node(int i)  
6.         :data(i),pNext(nullptr){}  
7.     ~node(){if(pNext)delete pNext;}  
8. };  
9. struct sl{  
10.     node* pHead;  
11.     node* pTail;  
12.     sl():pHead(nullptr),pTail(nullptr){}  
13.     ~sl(){if(pHead)delete pHead;}  
14.     void append(node* ps){  
15.         if(nullptr==pHead){  
16.             pHead=ps;  
17.             pTail=ps;  
18.         }  
19.         else{  
20.             pTail->pNext=ps;  
21.             pTail=ps;  
22.         }  
23.     }  
24.     void display(){  
25.         node* pCur=pHead;  
26.         while(pCur){  
27.             printf("%d\n",pCur->data);  
28.             pCur=pCur->pNext;  
29.         }  
30.     }  
31.     void revert(){  
32.         node* pCur=pHead;  
33.         if(pCur==pTail)return;  
34.         pTail=pHead;  
35.         node* pNext=nullptr;  
36.         while(pCur){  
37.             node* pPrev = pCur->pNext;  
38.             pCur->pNext = pNext;  
39.             if(pPrev==nullptr)break;  
40.             pNext=pCur;  
41.             pCur =pPrev;  
42.         }  
43.         pHead = pCur;  
44.     }  
45. };  
46. int _tmain(int argc, _TCHAR* argv[])  
47. {  
48.     sl list1;  
49.     list1.append(new node(2));  
50.     list1.append(new node(6));  
51.     list1.append(new node(8));  
52.     list1.append(new node(7));  
53.     list1.append(new node(5));  
54.     list1.display();  
55.     printf("reverted\n");  
56.     list1.revert();  
57.     list1.display();  
58.     return 0;  
59. }  

#include "stdafx.h"struct node{int data;node* pNext;explicit node(int i):data(i),pNext(nullptr){}~node(){if(pNext)delete pNext;}};struct sl{node* pHead;node* pTail;sl():pHead(nullptr),pTail(nullptr){}~sl(){if(pHead)delete pHead;}void append(node* ps){if(nullptr==pHead){pHead=ps;pTail=ps;}else{pTail->pNext=ps;pTail=ps;}}void display(){node* pCur=pHead;while(pCur){printf("%d\n",pCur->data);pCur=pCur->pNext;}}void revert(){node* pCur=pHead;if(pCur==pTail)return;pTail=pHead;node* pNext=nullptr;while(pCur){node* pPrev = pCur->pNext;pCur->pNext = pNext;if(pPrev==nullptr)break;pNext=pCur;pCur =pPrev;}pHead = pCur;}};int _tmain(int argc, _TCHAR* argv[]){sl list1;list1.append(new node(2));list1.append(new node(6));list1.append(new node(8));list1.append(new node(7));list1.append(new node(5));list1.display();printf("reverted\n");list1.revert();list1.display();return 0;}

 

[java] view plaincopyprint?

1. public class RevertList {  
2.   
3.     /** 
4.      * @param args 
5.      */  
6.     public static void main(String[] args) {  
7.         // TODO Auto-generated method stub  
8.         RevertList.list li=new RevertList.list();  
9.         li.append(2);  
10.         li.append(3);  
11.         li.append(5);  
12.         li.append(6);  
13.         li.append(10);  
14.         li.display();  
15.         System.out.println("================");  
16.         li.revert();  
17.         li.display();  
18.     }  
19.     static class node{  
20.         int data;  
21.         node next;  
22.         node(int d){  
23.             data=d;  
24.             next=null;  
25.         }  
26.     }  
27.     static class list{  
28.         node pHead;  
29.         node pTail;  
30.         list(){  
31.             pHead=pTail=null;  
32.         }  
33.         void append(int n){  
34.             if(null==pHead){  
35.                 pHead=new node(n);  
36.                 pTail=pHead;  
37.             }  
38.             else{  
39.                 pTail.next=new node(n);  
40.                 pTail=pTail.next;  
41.             }  
42.         }  
43.         void display(){  
44.             node Cur=pHead;  
45.             while(Cur!=null){//?  
46.                 System.out.println( "=" + Cur.data );  
47.                 Cur=Cur.next;  
48.             }  
49.         }  
50.         void revert(){  
51.             node Cur=pHead;  
52.             if(Cur==pTail){  
53.                 return;  
54.             }  
55.             pTail=pHead;  
56.             node Revert=null;  
57.             while(Cur!=null){  
58.                 node Next=Cur.next;  
59.                 Cur.next=Revert;  
60.                 if(Next==null)break;  
61.                 System.out.println("inside revert");  
62.                 Revert=Cur;  
63.                 Cur=Next;  
64.             }  
65.             pHead=Cur;  
66.         }  
67.     }  
68. }  

public class RevertList {/** * @param args */public static void main(String[] args) {// TODO Auto-generated method stubRevertList.list li=new RevertList.list();li.append(2);li.append(3);li.append(5);li.append(6);li.append(10);li.display();System.out.println("================");li.revert();li.display();}static class node{int data;node next;node(int d){data=d;next=null;}}static class list{node pHead;node pTail;list(){pHead=pTail=null;}void append(int n){if(null==pHead){pHead=new node(n);pTail=pHead;}else{pTail.next=new node(n);pTail=pTail.next;}}void display(){node Cur=pHead;while(Cur!=null){//?System.out.println( "=" + Cur.data );Cur=Cur.next;}}void revert(){node Cur=pHead;if(Cur==pTail){return;}pTail=pHead;node Revert=null;while(Cur!=null){node Next=Cur.next;Cur.next=Revert;if(Next==null)break;System.out.println("inside revert");Revert=Cur;Cur=Next;}pHead=Cur;}}}