本博客为《数据结构与算法-C语言版》（传智播客编著）的学习笔记，如涉及版权问题，请告知本人，本人会立即删除。

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
 
struct _Header
{
    int len;
    struct _Node* next;
};
struct _Node
{
    int data;
    struct _Node* next;
};
typedef struct _Header Head;
typedef struct _Node Node;

Head* CreteList()
{
    Head* ph=(Head*)malloc(sizeof(Head));
    if(ph!=NULL)
    {
        ph->len=0;
        ph->next=NULL;
        return ph;
    }
    return NULL;
}
Node* FindNodeByVal(Head* ph,int val)
{
    if(ph==NULL)
    {
        return NULL;
    }
    Node* pTmp=ph->next;
    do
    {
        if(pTmp->data==val)
        {
            return pTmp;
        }
        pTmp=pTmp->next;
    }while(pTmp->next!=ph->next);
    return NULL;
}

void CircleListInsert(Head* ph,int pos,int val)
{
    if(ph==NULL || pos<0 || pos>ph->len)
    {
        return;
    }
    
    Node* pval=(Node*)malloc(sizeof(Node));
    pval->data=val;
    
    if(ph->len==0)
    {
        ph->next=pval;
        pval->next=pval;
    }
    else
    {
        Node* pRear=ph->next;
        if(pos==0)
        {
            while(pRear->next!=ph->next)
            {
                pRear=pRear->next;
            }
            pval->next=ph->next;
            ph->next=pval;
            pRear->next=pval;
        }
        else
        {
            Node* pCur=ph->next;
            for(int i=1;i<pos;i++)
            {
                pCur=pCur->next;
            }
            pval->next=pCur->next;
            pCur->next=pval;
        }
    }
    ph->len++;
    return;
}

void CircleListDelete(Head* ph,int val)
{
    if(ph==NULL || ph->len==0)
    {
        return;
    }
    Node* pRear=ph->next;
    while(pRear->next!=ph->next)
    {
        pRear=pRear->next;
    }
    Node* pval=FindNodeByVal(ph, val);
    if(pval==NULL)
    {
        return;
    }
    if(pval==ph->next)
    {
        ph->next=pval->next;
        pRear->next=pval->next;
    }
    else
    {
        Node* pPre=ph->next;
        for(int i=0;i<ph->len;i++)
        {
            if(pPre->next==pval)
            {
                pPre->next=pval->next;
            }
            pPre=pPre->next;
        }
    }
    free(pval);
    ph->len--;
}
Node* FindNodeByPos(Head* ph,int pos)
{
    
    if(ph==NULL)
    {
        return NULL;
    }
    if(pos<0 || pos>ph->len)
    {
        return NULL;
    }
    Node* pTmp=ph->next;
    if(pTmp!=NULL)
    {
        for(int i=0;i<ph->len;i++)
        {
            if(i==pos)
            {
                return pTmp;
            }
            pTmp=pTmp->next;
        }
    }
    return NULL;
}

int main(int argc, const char * argv[]) {
    Head* ph=CreteList();
    CircleListInsert(ph, 0, 9);
    CircleListInsert(ph, 1, 6);
    CircleListInsert(ph, 2, 7);
    CircleListInsert(ph, 3, 8);
    CircleListInsert(ph, 4, 9);
    CircleListInsert(ph, 5, 10);
    CircleListDelete(ph, 9);
    CircleListDelete(ph, 8);
    for(int i=0;i<ph->len;i++)
    {
        printf("%d",FindNodeByPos(ph, i)->data);
    }

    
    return 0;
}