C语言—单链表

单链表操作：读取，插入和删除

 #include "stdafx.h"
 #include <string.h>
 #include <stdio.h>
 #include <stdlib.h>

 struct Node
 {
     int val;
     struct Node *next;
 };

 // build No head node
 struct Node * build_N_LinkList(int a[], int len)
 {
     struct Node * phead = NULL;  //struct Node * phead, last;
     struct Node * last = NULL;
     int k;
     for (k = ; k <=len-; k++)
     {
         struct Node * pnewnode = (struct Node *)malloc(sizeof(struct Node));
         pnewnode->val = a[k];
         pnewnode->next = NULL;
         if (k == )
         {
             phead = pnewnode;
             /*last->next = pnewnode;*/
             last = pnewnode;
         }
         else
     {
         last->next = pnewnode;
         last = pnewnode;
         }
     }
     return phead;
 }

 //build Head node
 struct Node *build_H_LinkList(int a[], int len )
 {
     struct Node * headnode = (struct Node *)malloc(sizeof(struct Node));
     int k;
     struct Node * phead = NULL;
     struct Node * plast = NULL;
     for (k = ; k <= len - ; k++)
     {
         struct Node * newnode = (struct Node *)malloc(sizeof(struct Node));
         newnode->val = a[k];
         newnode->next = NULL;
         if (k == )
         {
             headnode->next = newnode;
             phead = headnode;
             plast = newnode;
         }
         else
         {
             plast->next = newnode;
             plast = newnode;
         }
     }
     return phead;
 }

 // read with no head node
 int GetElem(struct Node *phead, int i)
 {
     int k = i;
     struct Node * p;
     p = phead;
     if (NULL==p) //这就是为什么很多时候常量（NULL）写在前面的原因，一旦写成“=”,编绎器就会报错，就可以直接看出来 ，你以后会经常看到这种写法
         return -;
     while (k != )
     {
         p = p -> next;
         --k;
     }
     return p->val;
 }

 //insert element before  ith. (no head node)//放在最后一个算插入么？？？
 int ListInsert_N (struct Node *phead, int a, int  i, int len)
 {
     int k =,m;
     struct Node *p = phead;
     struct Node *pr = phead;
     struct Node *newnode = (struct Node*)malloc(sizeof (struct Node));
     newnode->val = a;
     newnode->next = NULL;
     if (i <=  || i > len + ) //either first or last
         return -;
        else if (i==)  //first
        {
            newnode->next = p;
            pr = newnode;
        }
         else  //1 < i <= len+1,  middle&last
         {

             while (k<i-)
             {
                 p = p-> next;
                ++k;
             }
             newnode ->next = p->next;
             p->next = newnode;
         }
        len = len + ;
        for (m = ; m <= len; m++)
        {
            printf("%d\n", pr->val);
            pr = pr->next;
        }
     return ;
 }

 //insert element before  ith. (with head node)
 int ListInsert_H(struct Node *phead, int a, int i, int len)
 {
     struct Node * p = phead;
     struct Node * pr = phead;
     struct Node *newnode = (struct Node *)malloc(sizeof(struct Node));
     newnode->val = a;
     newnode->next = NULL;
     int k = ;
     int m;
     if (i <=  || i > len + )//
         return -;
     else
     {

         while (k  < i)//i==len+1 : add in last.
         {
             p = p ->next;
             ++k;
         }
         //此时p指向啥？第i个节点？k==i，退出循环，p指向i？
         newnode->next = p->next;
         p->next = newnode;
     }

     len = len + ;
     for (m = ; m <= len; m++)
     {
         pr = pr->next;
         printf("%d\n", pr->val);
     }
     return ;
 }

 // delete element before ith (No head node)
 int ListDelete_N(struct Node *phead, int i, int len)
 {
     int k;
     int m;
     struct Node *p = phead;
     struct Node *q = NULL;
     struct Node *pr = phead;
     if (i <=  || i > len)
         return -;
     else if (i == )
     {
         q = p;
         pr = p->next;
         free(q);
     }
     else
     {
         k = i-;
         while (k != )
         {
             p = p->next;
             --k;
         }
         q = p->next;
         p->next = q->next;
         free(q);
     }
     len = len - ;
     for (m = ; m <= len; m++)
     {
         printf("%d\n", pr->val);
         pr = pr->next;
     }
     return ;
 }

 //delete element before ith (Head node)
 int ListDelete_H(struct Node * phead, int i, int len)
 {
     struct Node *p = phead;
     struct Node *pr = phead;
     struct Node *q = NULL;
     int k,m ;
     if (i <=  || i > len)
         return -;
     else
     {
         k = i - ;
         while ( k != )
         {
             p = p->next;
             --k;
         }
         q = p->next;
         p->next = q->next;
         free(q);
     }
     len = len - ;
     for (m = ; m <= len; m++)
     {
         pr = pr->next;
         printf("%d\n", pr->val);
     }

 }

 int main()
 {
     int a[] = { ,,,, };
     int len,tmp;
     struct Node * phead;

     len = sizeof(a) / sizeof(a[]);   //注意：是sizeof(a),不是sizeof(a[])。
     phead = build_H_LinkList(a, len);  //注意：是a,不是a[]。
     //phead = build_N_LinkList(a, len);  //注意：是a,不是a[]。
     //ListInsert_H(phead,8,2,len);
     //ListInsert_N(phead, 8, 6, len);
     //ListDelete_N(phead, 5,len);
     ListDelete_H(phead, , len);
     //tmp = GetElem(phead, 3);
     //printf("%d\n", tmp);
 }