单链表操作总结

     这几天看欧立奇的《程序员面试宝典》，发现其中单链表的建立的程序存在错误，特别改正如下，原书的程序求的链表的长度要比正确的单链表的长度要多1。

在写程序时候，要特别注意if和while的区别。

   下面的程序是单链表的建立、插入、删除、逆序、排序、测长等程序代码，全部都调试通过（存在的问题在于，将链表的头指针看成了一个结点)。

#include <iostream>

using namespace std;

#include<malloc.h>

#define LEN sizeof(struct student)

typedef struct student

{

         int data;

         struct student *next;

}node;

struct student *creat()

{

         int data;

         int cycle =1;

         int n=0;

         struct student *head, *p_old, *p_new;

    p_old =(struct student *)malloc(LEN);

         while(cycle == 1)

         {

              printf("Please input the data \n");

             scanf("%d",&data);

                   if(data != 0)

                   {        

                            n=n+1;

                            if (n==1)

                            {

               head =p_old;

                               p_old ->data =data;

                               p_old ->next =NULL;

                            }

                            else

                            {

                              p_new=(struct student*)malloc(LEN);

                              p_new ->data =data;

                              p_old -> next =p_new;

                              p_old = p_new;

                            }

                   }

                   else

                   {

                            cycle = 0;                    

                   }

         }

         //head=head->next;

         p_old ->next =NULL;

         int b= head->next->next->data;       

         return head;

}

int length(struct student *head)

{

         struct student *p_start;

         int num =0;

         p_start=head;

 

         while (p_start !=NULL)

         {

                   num++;

                   p_start=p_start ->next;

         }

         return num;

}

void print(struct student *head)

{

         struct student *p_start;

         int n=length(head);

 

         p_start =head;

         for(int i=0;i<n;i++)

         {

                   cout<<p_start->data<<" ";

                   p_start =p_start->next;

         }

         cout<<endl;     //endl

}

node *del(struct student *head,int num)

{

         node *p_front;

         node *p_behind;

         p_front=head;

         //如果没有达到需要删除的数据，就继续移动指针指向，否则，进入下一段落

         //的if判断

         while(p_front->data != num && p_front->next !=NULL)

         {                 

                   p_behind=p_front;

                   p_front=p_front->next;

         }

         if (p_front->data==num)

         {

                   if (p_front==head)

                   {

                            head = p_front->next;

                            free(p_front);

                   }

                   else

                   {

                            p_behind->next = p_front->next;

                            free(p_front);

                   }

         }

         return head;

}

node *insert(node *head,int num)

{

         node *p_behind,*p_front,*p_new;

         p_front = head;

         p_new = (node *)malloc(LEN);

         p_new->data = num;

 

         while(p_front->data < num && p_front->next != NULL)

         {

                   p_behind = p_front;

                   p_front = p_front->next;

         }

         if(p_front->data >= num)

         {

                   if(p_front==head)

                   {

                            p_new->next = p_front;

                            head = p_new;

                   }

                   else if(p_front != head && p_front->next != NULL)

                   {

                            p_behind->next =p_new;

                            p_new->next = p_front;

                   }

         }

         else

         {

                   p_front->next = p_new;

                   p_new->next = NULL;

         }

         return head;

}

node *sort(node *head)

{

         node *p;

         int n;

         if(head==NULL || head->next ==NULL)

         {

                   return head;

         }

         n=length(head);

         int temp;

         for(int i=1;i<n;i++)

         {

                   p=head;

                   for(int j=0;j<n-i;j++)

                   {

                            if(p->data < p->next->data)

                            {

                                     temp =p->next->data;

                                     p->next->data =p->data;

                                     p->data=temp;

                            }

                            p=p->next;

                   }

         }

         return head;

} 

node *reverse(node *head)

{

         node *p,*q,*r;

         p=head;

         q=p->next;

    

    while(q != NULL)

         {

                   r =q->next;

                   q->next = p;

                   p = q;

                   q =r;

         }

         head ->next;

         head = p;

         return head;

} 

void main()

{

         struct student *head;

         int len;

         int num = 12;

         head =(struct student *)malloc(sizeof( struct student));

         head = creat();

         len = length(head);  

         print(head);

         head = insert(head,20); 

         print(head);

         head =sort(head);

         print(head);

         head =reverse(head);

         int b=head->next->data;

}