C語言實現不帶頭結點鏈表的基本操作

typedef :起別名，可以方便修改數據型別
#include<stdio.h>
typedef struct node
{
        int num;
        struct node *pNext;
}Node_t,*pNode_t;
typedef struct {
        Node_t num;//數據
        pNode_t phead = NULL;//指針
}

一、不帶頭結點的鏈表的頭尾插法

頭插法：首先判斷頭指針是否爲空，如果爲空，將首尾指針指向新節點，如果不爲空，則將新節點的指針指向首節點，然後首指針指向首節點。

void headInsert(pNode_t *ppHead, pNode_t *ppTail, int num)
{
        pNode_t pNew = (pNode_t)calloc(1, sizeof(Node_t));
        pNew->num = num;
        if (*ppHead== NULL)
        {
               *ppHead = pNew;
               *ppTail = pNew;
        }
        else
        {
               pNew->pNext = *ppHead;
               *ppHead = pNew;
        }
}

尾插法：同頭插法一樣，判斷首指針是否爲空，爲空，首尾節點指向新節點，不空，將尾節點連線新節點，然後尾指針指向新節點

void tailInsert(pNode_t *ppHead, pNode_t *ppTail, int num)
{
        pNode_t pNew = (pNode_t)calloc(1, sizeof(Node_t));
        pNew->num = num;
        if (*ppHead == NULL)
        {
               *ppHead = pNew;
               *ppTail = pNew;
        }
        else
        {
               (*ppTail)->pNext = pNew;
               *ppTail = pNew;
        }
}

二、不帶頭節點鏈表的有序插入

鏈表的有序插入：先判斷首指針是否爲空，爲空，首尾指針指向新節點，然後新節點插入有三種對應情況，第一種，新節點小於首節點，頭插法插在首節點前，第二種，新節點排在鏈表中間，使用pre和cur指針來判斷新節點的位置，第三種，新節點大於尾結點，使用尾插法插在尾結點後。

void sortInsert(pNode_t *ppHead, pNode_t *ppTail, int num)
{
        pNode_t pNew = (pNode_t)calloc(1, sizeof(Node_t));
        pNew->num = num;
        if (*ppHead==NULL)
        {
               *ppHead = pNew;
               *ppTail = pNew;
        }
        else if (pNew->num < (*ppHead)->num)
               {
                       pNew->pNext = *ppHead;
                       *ppHead = pNew;
               }
        else
        {
               pNode_t pPre = *ppHead;
               pNode_t pCur = pPre->pNext;
               while (pCur)
               {
                       //if (pNew->num<pCur->num&&pNew->num>pPre->num)
                       if (num < pCur->num) //因爲鏈表有序且指針遍歷，所以只要找到num大於pCur對應值的節點就行。
                       { 
                              pNew->pNext = pCur;
                              pPre->pNext = pNew;
                              break;
                       }
                       pPre = pCur;
                       pCur = pCur->pNext;
               }
               if (pCur == NULL)
               {
                       (*ppTail)->pNext = pNew; 
                       *ppTail = pNew;
               }
        }
}

三、不帶頭結點鏈表的增刪查改

鏈表的查改：用pcur一次次遍歷

void listModefiy(pNode_t *ppHead, int findNum, int changeNum)
{//這裏傳入的是二級指針，但因爲不用修改指針的指向，只需修改值，傳入一級指針也是可以的,然後在主函數中不用取地址傳入。(pNode_t pHead,int findNum,int changeNum),
        pNode_t pCur = *ppHead;
        while (pCur)
        {
               if (pCur->num == findNum)
               {
                       pCur->num = changeNum;
                       break;
               }
               pCur = pCur->pNext;
        }
        if (pCur == NULL)
        {
               printf("there are't no value here");
        }
}

鏈表的刪除：先檢查鏈表是否爲空，爲空返回，不爲空，則判斷首節點是否爲刪除的節點，如果是，將首指針向後移動並且保證首指針不指向NULL，還是設立pre和cur指針遍歷找到待刪除節點。最後記得free(pCur),pCur=NULL；避免懸空指針。

void deleteNum(pNode_t *ppHead,pNode_t *ppTail,int dNum)
{
        pNode_t pCur = *ppHead;
        if (pCur== NULL)
        {
               printf("This list is empty!\n");
               return ;
        }
        else if(pCur->num==dNum)
        {
               *ppHead = pCur->pNext;
               if (*ppHead == NULL)
               {
                       *ppTail = NULL;
               }
        else
        {
               pNode_t pPre = *ppHead;
               pCur = pPre->pNext;
               while (pCur)
               {
                       if (pCur->num == dNum)
                       {
                              pPre->pNext = pCur->pNext;
                              break;
                       }
                       pPre = pCur;
                       pCur = pCur->pNext;
               }
               if (pCur == *ppTail)
               {
                       *ppTail = pPre;
               }
               if(pCur==NULL)
               {
                       printf("There are not value here\n");
                       return;
               }
        }
               free(pCur);
               pCur == NULL;
               
}