user-0 提问: C双链表的逆序操作

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user: user-1
content: 单步跟踪程序执行，观察每一步变量变化情况，就容易理解了

user: user-2
content: 数据结构对单链表进行数据排序 http://bbs.csdn.net/topics/392201633

user: user-2

user: user-2
content: 仅供参考：//不带表头结点的双向链表 #include <stdio.h> #include <stdlib.h> #include <malloc.h> #include <time.h> #include <locale.h> struct NODE {     int          data;     struct NODE *next;     struct NODE *prev; } *head,*p,*q,*s,*p1,*p2,*q1,**ta; int i,k,n,t,m,v,N=10; int main() {     setlocale(LC_ALL,"chs");     srand(time(NULL));      head=NULL;      printf("创建%d个节点的双向链表:",N);//创建N个节点的双向链表     p=head;     for (i=0;i<N;i++) {         q=(struct NODE *)malloc(sizeof(struct NODE));         if (NULL==q) exit(1);         q->data=rand()%100;//填写0..99的随机值         q->next=NULL;         q->prev=NULL;         if (NULL==p) {             head=q;             p=head;         } else {             p->next=q;             q->prev=p;             p=q;         }     }      //输出整个双向链表     s=head;     while (1) {         if (NULL==s) {             printf("\n");             break;         }         printf("%02d<->",s->data);         if (NULL!=s->next && s->next->prev!=s) {printf(" !\n");break;}         s=s->next;     }      k=3;     v=5;     printf("将值为%d的结点插入到双向链表的第%d个结点前:",v,k);//将值为v的结点插入到双向链表的第k个结点前     n=0;     p=head;     while (1) {         if (NULL==p) {             break;         }         n++;         if (k==1) {             q=(struct NODE *)malloc(sizeof(struct NODE));             if (NULL==q) exit(1);             q->data=v;             q->next=head;             q->prev=NULL;             head->prev=q;             head=q;             break;         } else {             if (k-1==n) {                 q=(struct NODE *)malloc(sizeof(struct NODE));                 if (NULL==q) exit(1);                 q->data=v;                 q->next=p->next;                 q->prev=p;                 p->next->prev=q;                 p->next=q;                 break;             }         }         p=p->next;     }      //输出整个双向链表     s=head;     while (1) {         if (NULL==s) {             printf("\n");             break;         }         printf("%02d<->",s->data);         if (NULL!=s->next && s->next->prev!=s) {printf(" !\n");break;}         s=s->next;     }      k=5;     printf("删除第%d个节点:",k);//删除第k个节点     n=0;     p=head;     while (1) {         if (NULL==p) {             break;         }         n++;         if (k==1) {             q=head;             head=head->next;             head->prev=NULL;             free(q);             break;         } else {             if (k-1==n) {                 q=p->next;                 if (q) {                     p->next=q->next;                     if (q->next) q->next->prev=p;                     free(q);                 }                 break;             }         }         p=p->next;     }      //输出整个双向链表     s=head;     while (1) {         if (NULL==s) {             printf("\n");             break;         }         printf("%02d<->",s->data);         if (NULL!=s->next && s->next->prev!=s) {printf(" !\n");break;}         s=s->next;     }      printf("从小到大排序:");//从小到大排序     for (p=head,p1=NULL;p!=NULL;p1=p,p=p->next) {         for (q=p->next,q1=p;q!=NULL;q1=q,q=q->next) {             if (p->data > q->data) {                  //交换data //              printf("swap %02d %02d\n",p->data,q->data); //              t=p->data;p->data=q->data;q->data=t;                  //或者                  //交换prev和next //              printf("swap %02d %02d\n",p->data,q->data);                 if (p==head) {//p是头                     if (p->next==q) {//pq挨着                         head=q;                         head->prev=NULL;                         p->next=q->next;                         p->prev=q;                         if (q->next) q->next->prev=p;                         q->next=p;                         q=p;                         p=head;                     } else {//pq不挨着                         head=q;                         head->prev=NULL;                         p2=p->next;                         p->next=q->next;                         p->prev=q->prev;                         if (q->next) q->next->prev=p;                         q->next=p2;                         p2->prev=q;                         q1->next=p;                         q=p;                         p=head;                     }                 } else {//p不是头                     if (p->next==q) {//pq挨着                         p1->next=q;                         p->next=q->next;                         p->prev=q;                         if (q->next) q->next->prev=p;                         q->next=p;                         q->prev=p1;                         q=p;                         p=p1->next;                     } else {//pq不挨着                         p1->next=q;                         p2=p->next;                         p->next=q->next;                         p->prev=q->prev;                         if (q->next) q->next->prev=p;                         q->next=p2;                         p2->prev=q;                         q->prev=p1;                         q1->next=p;                         q=p;                         p=p1->next;                     }                 }                  //输出整个双向链表 //              s=head; //              while (1) { //                  if (NULL==s) { //                      printf("\n"); //                      break; //                  } //                  printf("%02d<->",s->data); //                  if (NULL!=s->next && s->next->prev!=s) {printf(" !\n");break;} //                  s=s->next; //              } //              getchar();             }         }     }      //输出整个双向链表并计算链表长度n     n=0;     s=head;     while (1) {         if (NULL==s) {             printf("\n");             break;         }         printf("%02d<->",s->data);         if (NULL!=s->next && s->next->prev!=s) {printf(" !\n");break;}         n++;         s=s->next;     }      printf("将整个链表逆序:");//将整个链表逆序     if (n>=2) {         p=head;         q=p->next;         p->next=NULL;         while (1) {             q1=q->next;             q->next=p;             p->prev=q;             p=q;             q=q1;             if (NULL==q) break;         }         head=p;         head->prev=NULL;     }      //输出整个双向链表     s=head;     while (1) {         if (NULL==s) {             printf("\n");             break;         }         printf("%02d<->",s->data);         if (NULL!=s->next && s->next->prev!=s) {printf(" !\n");break;}         s=s->next;     }      m=4;     n=6;     printf("将双向链表中前%d个结点和后%d个结点进行互换:",m,n);//将双向链表中前m个结点和后n个结点进行互换,m+n为链表总长     k=0;     p=head;     while (1) {         if (NULL==p) {             break;         }         k++;         if (m==k) {             q=p;         }         s=p;         p=p->next;     }     q1=head;     head=q->next;     head->prev=NULL;     s->next=q1;     q1->prev=s;     q->next=NULL;      //输出整个双向链表     s=head;     while (1) {         if (NULL==s) {             printf("\n");             break;         }         printf("%02d<->",s->data);         if (NULL!=s->next && s->next->prev!=s) {printf(" !\n");break;}         s=s->next;     }      //释放所有节点     p=head;     while (1) {         if (NULL==p) {             break;         }         q=p->next;         free(p);         p=q;     }      return 0; } //创建10个节点的双向链表:93<->03<->60<->05<->57<->71<->02<->41<->26<->85<-> //将值为5的结点插入到双向链表的第3个结点前:93<->03<->05<->60<->05<->57<->71<->02<->41<->26<->85<-> //删除第5个节点:93<->03<->05<->60<->57<->71<->02<->41<->26<->85<-> //从小到大排序:02<->03<->05<->26<->41<->57<->60<->71<->85<->93<-> //将整个链表逆序:93<->85<->71<->60<->57<->41<->26<->05<->03<->02<-> //将双向链表中前4个结点和后6个结点进行互换:57<->41<->26<->05<->03<->02<->93<->85<->71<->60<-> //

user: user-3
content: #include<stdio.h> #include <malloc.h>  typedef struct Node {     int element;     struct Node *next; }Node;  Node * Create(int n) {     Node *head,*p,*tail,*q;     int i,x;      head = NULL;     tail = NULL;     q = NULL;     for(i=0;i<n;i++)     {         p=(Node *)malloc(sizeof(Node));         printf("输入一个数:  \n");         scanf("%d", &x);         p->element = x;         p->next = NULL;         if(NULL==head)             head = p;         else             tail->next = p;         tail = p;          if (i == n)             p->next = q;     }     return head;  } void print(Node * head) {     Node *p;     p = head;     if(!head) {         printf("链表为空！\n");     } else {         printf("如下所示：\n");         while(p) {             printf("%d ",p->element);             p = p->next;         }     }     putchar(10); }  Node * Inverse(Node * head) {     Node *p, *q, *s;      if(!head)         return NULL;      p = head;     s = head->next;     head->next = NULL;      while (s) {         q = s->next;         s->next = p;         p = s;         s = q;         /*        Node *r;         r = p;         while (r) {             printf("%d\t", r->element);             r = r->next;         }         putchar(10);         */     }      return p;  } int main() {     Node *head;     int x;     printf("链表内有几个数： \n");     scanf("%d",&x);     head = Create(x);     print(head);     head = Inverse(head);     printf("逆转后的链表为：");     print(head);     return 0; } 链表逆序，参考一下吧

user: user-0
content: 弄明白了，谢谢提示！

user: user-4
content: r不是NULL，你拿个笔，纸，画画就知道了

user: user-5
content: r为什么是NULL