什麼是無頭結點連結串列？？？

singlelinkedlist.h標頭檔案

#ifndef __SINGLELINKEDLIST_H__
#include<stdio.h>
#include<windows.h>
#include<assert.h>
typedef int DataType;

typedef struct ListNode
{
    DataType data;
    struct ListNode *next;

}ListNode;

ListNode *InitList(DataType num);//初始化並賦值
void
 
 PushBack(ListNode **pplist, DataType num);//尾插
void PrintList(ListNode *plist);//輸出
void PopBack(ListNode **pplist);//尾刪
void PushFront(ListNode **pplist, DataType num);//頭插
void PopFront(ListNode **pplist);//頭刪
ListNode* Find(ListNode *plist, DataType num);//查詢
void Insert(ListNode** pplist, ListNode* pos, DataType x);//插入
 

void Erase(ListNode** pplist, ListNode* pos);//刪除


#endif//__SINGLELINKEDLIST_H__

singlelinkedlist.c實現部分

#include "singlelinkedlist.h"


ListNode *InitList(DataType num)//定義一個新的結點
{
    ListNode *node = (ListNode*)malloc(sizeof(ListNode));
    node->data = num;
    node->next = NULL;
    return node;
}
void
 
 PushBack(ListNode **pplist, DataType num)//尾插
{

    if (*pplist == NULL)//空連結串列
    {
        *pplist = InitList(num);//定義一個結點
    }
    else if ((*pplist)->next == NULL)//只有一個結點
    {
        (*pplist)->next = InitList(num);
    }
    else//正常情況(多個結點)
    {
        ListNode *tail = *pplist;
        while (tail->next)
        {
            tail = tail->next;//依次指向下一個結點，找到為空的尾結點
        }
        tail->next = InitList(num);//找到以後直接新增一個結點
    }
}


void PrintList(ListNode *plist)//列印連結串列
{
    ListNode *tail = plist;
    while (tail)
    {
        printf("%d->", tail->data);
        tail = tail->next;
    }
    printf("NULL");
    printf("\n");
}


void PopBack(ListNode **pplist)//尾刪
{
    if (*pplist == NULL)//空連結串列
    {
        return;
    }
    else if ((*pplist)->next == NULL)//只有一個結點，直接釋放
    {
        free(*pplist);
        *pplist = NULL;
    }
    else
    {
        ListNode* tail = *pplist;
        ListNode* pos = tail;
        while (tail->next)//tail指向pos的後一個結點
        {
            pos = tail; 
            tail = tail->next;
        }
        free(tail);//釋放最後一個結點就相當於刪除了尾結點
        tail = NULL;
        pos->next = NULL;
    }
}

void PushFront(ListNode **pplist, DataType num)//頭插
{
    if (*pplist == NULL)//空連結串列
    {
        *pplist = InitList(num);
    }
    else
    {
        ListNode *tmp = InitList(num);//開闢一個新的結點
        tmp->next = *pplist;//讓它指向原先的開始結點
        *pplist = tmp;//pplist依然開始結點
    }
}

void PopFront(ListNode **pplist)//頭刪
{
    if (*pplist == NULL)//空連結串列
    {
        return;
    }
    else if ((*pplist)->next == NULL)//只有一個結點
    {
        *pplist = NULL;
    }
    else
    {
        ListNode *tmp = (*pplist)->next;//tmp指向原先頭結點指向的下一個位置
        free(*pplist);
        *pplist = tmp;
    }

}

ListNode* Find(ListNode *plist, DataType num)//查詢
{
    assert(plist);//斷言其是否為空連結串列
    while (plist)
    {
        if (plist->data == num)
        {
            return plist;
        }
        plist = plist->next;
    }
    return NULL;
}


void Insert(ListNode** pplist, ListNode* pos, DataType num)//插入
{
    assert(*pplist&&pos);
    if (((*pplist)->next == NULL) || (pos == *pplist))
        //只有開始結點或者是要插入的正好在開始結點的前面
    {
        PushFront(pplist, num);
    }
    else
    {
        ListNode* tmp = NULL;
        ListNode* tail = *pplist;
        while (tail->next != pos)
        {
            tail = tail->next;
        }
        tmp = InitList(num);
        tail->next = tmp;
        tmp->next = pos;
    }
}

void Erase(ListNode** pplist, ListNode* pos)//刪除
{
    assert(*pplist&&pos);
    if (((*pplist)->next == NULL) || (*pplist == pos))
    {
        PopFront(pplist);
    } 
    else
    {
        ListNode* tmp = *pplist;
        while (tmp->next != pos)
        {
            tmp = tmp->next;
        }
        tmp->next = pos->next;
        free(pos);
        pos = NULL;
    }
}

test.c測試部分

#include "singlelinkedlist.h"



void test()
{
    ListNode *list = NULL;
    PushBack(&list, 1);
    PushBack(&list, 2);
    PushBack(&list, 3);
    PushBack(&list, 4);
    PrintList(list);
    PopBack(&list);
    PrintList(list);
    PopBack(&list);
    PrintList(list);
    PopBack(&list);
    PrintList(list);
    PopBack(&list);
    PrintList(list);
}



void test1()
{
    ListNode *list = NULL;
    PushFront(&list, 1);
    PushFront(&list, 2);
    PushFront(&list, 3);
    PushFront(&list, 4);
    PushFront(&list, 5);
    PrintList(list);
    PopFront(&list);
    PrintList(list);
    PopFront(&list);
    PrintList(list);
    PopFront(&list);
    PrintList(list);
    PopFront(&list);
    PrintList(list);
    PopFront(&list);
    PrintList(list);
}


void test2()
{
    ListNode *list = NULL;
    PushFront(&list, 1);
    PushFront(&list, 2);
    PushFront(&list, 4);
    PushFront(&list, 5);
    PushFront(&list, 6);
    PrintList(list);
    ListNode *ret = Find(list, 2);
    //測試使用
    /*if (ret != NULL)
    {
        printf("%p\n", ret);
    }
    else
    {
        printf("沒有這個值!\n");
    }*/
    Insert(&list, ret, 3);
    PrintList(list);
    Erase(&list, ret);
    PrintList(list);

}


int main()
{
    //test();
    //test1();
    test2();
    system("pause");
    return 0;
}

test()測試結果

test1()測試結果

test2()測試結果

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