循環鏈表的插入刪除實現

循環鏈表的插入、刪除

循環鏈表的插入示意：

循環鏈表的刪除示意：

typedef void CircleList;

typedef struct _tag_CircleListNode
{
    struct _tag_CircleListNode * next;
}CircleListNode;

typedef struct _tag_CircleList
{
    CircleListNode header;
    CircleListNode* slider;
    int length;
}TCircleList;

//插入，對應第一幅示意圖
int CircleList_insert(CircleList* list, CireListNode* node, int pos)
{
    int ret = 0, i=0;
    TCircleList* sList = (TCircleList*)list;

    if (list == NULL || node== NULL || pos<0)
    {
        return -1;
    }

    CircleListNode* current = (CircleListNode*)sList;

        for(i=0; (i<pos) && (current->next != NULL); i++)
        {
            current = current->next;
        }

        //current->next 0號節點的地址
        node->next = current->next; //1
        current->next = node; //2

        //若第一次插入節點
        if( sList->length == 0 )
        {
            sList->slider = node;
        }

        sList->length++;

        //若頭插法 current仍然指向頭部
        //（原因是：跳0步，沒有跳走） 中間第一種情況
        if( current == (CircleListNode*)sList )
        {
            //獲取最後一個元素
            CircleListNode* last = CircleList_Get(sList, sList->length - 1); 
            last->next = current->next; //3
        }

        return ret;
}

CircleListNode* CircleList_Get(CircleList* list, int pos) // O(n)
{
    TCircleList* sList = (TCircleList*)list;
    CircleListNode* ret = NULL;
    int i = 0;

    if (list==NULL || pos<0)
    {
        return NULL;
    }

    {
        CircleListNode* current = (CircleListNode*)sList;

        for(i=0; i<pos; i++)
        {
            current = current->next;
        }

        ret = current->next;
    }

    return ret;
}

//刪除，對應第二幅圖
CircleListNode* CircleList_Delete(CircleList* list, int pos) // O(n)
{
    TCircleList* sList = (TCircleList*)list;
    CircleListNode* ret = NULL;
    int i = 0;

    if( (sList != NULL) && (pos >= 0) && (sList->length > 0) )
    {
        CircleListNode* current = (CircleListNode*)sList;
        CircleListNode* last = NULL;

        for(i=0; i<pos; i++)
        {
            current = current->next;
        }

        //若刪除第一個元素（頭結點）左上
        if( current == (CircleListNode*)sList )
        {
            last = (CircleListNode*)CircleList_Get(sList, sList->length - 1);
        }

        //求要刪除的元素  右上 左上
        ret = current->next;
        current->next = ret->next;

        sList->length--;

        //判斷鏈表是否爲空
        if( last != NULL )
        {
            sList->header.next = ret->next;
            last->next = ret->next;
        }

        //若刪除的元素爲遊標所指的元素
        if( sList->slider == ret )
        {
            sList->slider = ret->next;
        }

        //若刪除元素後，鏈表長度爲0
        if( sList->length == 0 )
        {
            sList->header.next = NULL;
            sList->slider = NULL;
        }
    }

    return ret;
}

總結

循環鏈表的插入：注意第一次插入的條件判斷（維護遊標）；只有一個頭結點的插入；
循環鏈表的刪除：注意刪除第一個元素（頭結點）；current->next = current->next->next;不需要考慮鏈表是否爲空，而last->next = ret->next;需要考慮，即爲第一個節點的刪除。