无头节点单链表的操作

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


//初始化单链表
void InitList(LNode **head)
{
    if(head == NULL)
    {
        printf("head is empty");
        return;
    }
    (*head) = NULL;
}

//尾插法建立单链表
void InsertListTail(LNode **head,int val)
{
    if(head == NULL)
    {
        printf("head is empty!\n");
        return;
    }
    if(*head == NULL)
    {
        LNode *s = (LNode*)malloc(sizeof(LNode));
        if(s == NULL)
        {
            printf("apply fail!\n");
            return;
        }
        s->data = val;
        s->next = NULL;
        *head = s;
        return;
    }
    LNode *p = *head;
    while(p->next != NULL)
    {
        p = p->next;
    }
    LNode *s = (LNode*)malloc(sizeof(LNode));
    if(s == NULL)
    {
        printf("apply fail!\n");
        return;
    }
    s->next = p->next;
    p->next = s;
    s->data = val;
}
//头插法建立单链表
void InsertListHead(LNode **head,int val)
{
    if(head == NULL)
    {
        printf("head is empty!\n");
        return;
    }
    LNode *p = (LNode*)malloc(sizeof(LNode));
    if(p == NULL)
    {
        printf("apply fail!\n");
        return;
    }
    p->data = val;
    p->next = (*head);
    (*head) = p;
}

//显示单链表中的信息
void ShowList(LNode **head)
{
    if(head == NULL)
    {
        printf("head is empty!\n");
        return;
    }
    LNode *p = (*head);
    while(p != NULL)
    {
        printf("%d ",p->data);
        p = p->next;
    }
    printf("\n");
}

//销毁单链表
void DestoryList(LNode **head)
{
    if(head == NULL)
    {
        printf("head is empty!\n");
        return;
    }
    LNode *p;
    while(*head != NULL)
    {
        p = (*head)->next;
        free(*head);
        *head = p;
    }
}
//头删
void DeleteListHead(LNode **head)
{
    if(head == NULL)
    {
        printf("head is empty!\n");
        return;
    }

    if(*head == NULL)
    {
        printf("单链表中无结点，无法删除！\n");
        return;
    }
    LNode *p = *head;
    LNode *q = p->next;
    *head = q;
    free(p);
}

//尾删
void DeleteListTail(LNode **head)
{
    if(head == NULL)
    {
        printf("head is empty!\n");
        return;
    }
    if(*head == NULL)
    {
        printf("单链表中无结点，无法删除！\n");
        return;
    }
    LNode *p = *head;
    LNode *q = p->next;
    while(q->next != NULL)
    {
        p = q;
        q = q->next;
    }
    p->next = NULL;
    free(q);
}
//按位置删除
void ListDeletePos(LNode **head,int pos)
{
    if(head == NULL)
    {
        printf("head is empty！\n");
        return ;
    }
    if(*head == NULL)
    {
        printf("单链表中无头节点，无法删除");
        return;
    }
    if(pos <= 0)
    {
        printf("删除位置不对!\n");
        return;
    }
    LNode *p = *head;
    LNode *q = p->next;
    while(--pos && q->next != NULL)
    {
        p = q;
        q = q->next;
    }
    *head = q;
    free(p);
}

//按位置插入数据
void ListInsertPos(LNode **head,int val,int pos)
{
    LNode *s = (LNode*)malloc(sizeof(LNode));
    if(s == NULL)
    {
        printf("申请结点失败！\n");
        return;
    }
    s->data = val;
    if(head == NULL)
    {
        printf("head is empty!\n");
        return;
    }
    if(pos <= 0)
    {
        printf("插入位置不正确，不能进行插入！\n");
        return;
    }
    if(*head == NULL)
    {
        s->next = *head;
        *head = s;
    }
    if(pos == 1)
    {
        LNode *c = *head;
        *head = s;
        s->next = c->next;
        return;
    }
    LNode *p = *head;
    LNode *q = p->next;
    while((pos-2) > 0 && q != NULL)
    {
        p = q;
        q = q->next;
        --pos;
    }
    if(q == NULL)
    {
        printf("插入位置不正确，不能进行插入！\n");
        return;
    }
    s->next = p->next;
    p->next = s;
}