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 = 0; k <=len-1; k++)
    {
        struct Node * pnewnode = (struct Node *)malloc(sizeof(struct Node));
        pnewnode->val = a[k];
        pnewnode->next = NULL;
        if (k == 0)
        {
            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 = 0; k <= len - 1; k++)
    {
        struct Node * newnode = (struct Node *)malloc(sizeof(struct Node));
        newnode->val = a[k];
        newnode->next = NULL;
        if (k == 0)
        {
            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 -1;   
    while (k != 1)
    {
        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 =1,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 <= 0 || i > len + 1) //either first or last
        return -1;
       else if (i==1)  //first
       {
           newnode->next = p;
           pr = newnode;
       }
        else  //1 < i <= len+1,  middle&last
        {
                     
            while (k<i-1)
            {
                p = p-> next;
               ++k;
            }
            newnode ->next = p->next;
            p->next = newnode;
        }
       len = len + 1;  
       for (m = 1; m <= len; m++)
       {
           printf("%d
", pr->val);
           pr = pr->next;
       }
    return 0;
}

//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 = 1;
    int m;
    if (i <= 0 || i > len + 1)//
        return -1;
    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 + 1;
    for (m = 1; m <= len; m++) 
    {    
        pr = pr->next;
        printf("%d
", pr->val);
    }
    return 0;
}

// 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 <= 0 || i > len)
        return -1;
    else if (i == 1)
    {
        q = p;
        pr = p->next;
        free(q);
    }
    else
    {
        k = i-1;
        while (k != 1)
        {
            p = p->next;
            --k;
        }
        q = p->next;
        p->next = q->next;
        free(q);
    }
    len = len - 1;
    for (m = 1; m <= len; m++)
    {
        printf("%d
", pr->val);
        pr = pr->next;
    }
    return 0;
}

//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 <= 0 || i > len)
        return -1;
    else
    {
        k = i - 1;
        while ( k != 0)
        {
            p = p->next;
            --k;
        }
        q = p->next;
        p->next = q->next;
        free(q);
    }
    len = len - 1;
    for (m = 1; m <= len; m++)
    {
        pr = pr->next;
        printf("%d
", pr->val);
    }

}

int main()
{
    int a[] = { 1,2,3,4,5 };
    int len,tmp;
    struct Node * phead;

    len = sizeof(a) / sizeof(a[0]);   //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, 1, len);
    //tmp = GetElem(phead, 3);
    //printf("%d
", tmp);
}