SkipList跳表的实现

关键的是要理解Node结构中使用的柔性数组（代码的55行）。

/*************************************************************************    > File Name: skiplist.cpp    > Author: Summer    > Mail: [e-mail]    > Created Time: Mon 25 Jul 2016 03:19:38 PM CST ************************************************************************/#include <iostream>#include <stdio.h>#include <stdlib.h>#include <assert.h>using namespace std;template<class KEY_TYPE, class VAL_TYPE>class CSkipList{private:    struct Node;public:    CSkipList(unsigned int uiMaxLevel);    ~CSkipList();    bool Insert(KEY_TYPE key, VAL_TYPE value);    bool Erase(KEY_TYPE key);    VAL_TYPE* Search(KEY_TYPE key);public:    class Iterator    {    public:        explicit Iterator(const CSkipList* list);        const KEY_TYPE& Key() const;        VAL_TYPE* Value() const;        bool Next();        bool IsEnd() const;    private:        const CSkipList *m_poList;        struct Node* m_pstNode;    };private:   struct Node *NewNode(int iLevel);   unsigned int RandomLevel();private:    unsigned int m_uiMaxLevel;    unsigned int m_uiLevel;    Node *m_pstHead;};template<class KEY_TYPE, class VAL_TYPE>struct CSkipList<KEY_TYPE, VAL_TYPE>::Node{    KEY_TYPE key;    VAL_TYPE value;    Node* next[1]; // Flexible Array};template<class KEY_TYPE, class VAL_TYPE>CSkipList<KEY_TYPE, VAL_TYPE>::CSkipList(unsigned int uiMaxLevel){    m_uiMaxLevel = uiMaxLevel > 0 ? uiMaxLevel : 2;    m_uiLevel = 0;    m_pstHead = NewNode(m_uiMaxLevel - 1);    assert(m_pstHead);     for (unsigned i = 0; i < uiMaxLevel; ++i)    {        m_pstHead->next[i] = NULL;    }}template<class KEY_TYPE, class VAL_TYPE>CSkipList<KEY_TYPE, VAL_TYPE>::~CSkipList(){    Node *p = m_pstHead;    Node *next = NULL;    while(p)    {        next = p->next[0];        free(p);        p = next;    }}template<class KEY_TYPE, class VAL_TYPE>typename CSkipList<KEY_TYPE, VAL_TYPE>::Node* CSkipList<KEY_TYPE, VAL_TYPE>::NewNode(int iLevel){    Node *p = (Node*)malloc(sizeof(Node) + iLevel*sizeof(Node*));    return p;}template<class KEY_TYPE, class VAL_TYPE>unsigned int CSkipList<KEY_TYPE, VAL_TYPE>::RandomLevel(){    unsigned int uiLevel = 1;    while(rand()%2)    {        ++uiLevel;    }    uiLevel = uiLevel > m_uiMaxLevel ? m_uiMaxLevel : uiLevel;    return uiLevel;}template<class KEY_TYPE, class VAL_TYPE>bool CSkipList<KEY_TYPE, VAL_TYPE>::Insert(KEY_TYPE key, VAL_TYPE value){    Node *p = NULL, *q = NULL;    Node *update[m_uiMaxLevel];    p = m_pstHead;    int i = m_uiLevel;    for (; i >= 0; --i)    {        while((q=p->next[i]) && q->key < key)        {            p = q;        }        update[i] = p;    }    if (q && q->key == key)    {        q->value = value;        return true;    }    unsigned int uiLevel = RandomLevel();    if (uiLevel > m_uiLevel)    {        for (i = m_uiLevel; i < uiLevel; ++i)        {            update[i] = m_pstHead;        }        m_uiLevel = uiLevel;    }    q = NewNode(uiLevel);    if (NULL == q)    {        return false;    }    q->key = key;    q->value = value;    for (i = uiLevel - 1; i >= 0; --i)    {        q->next[i] = update[i]->next[i];        update[i]->next[i] = q;    }    return true;}template<class KEY_TYPE, class VAL_TYPE>bool CSkipList<KEY_TYPE, VAL_TYPE>::Erase(KEY_TYPE key){    Node *update[m_uiMaxLevel];    Node *q = NULL, *p = m_pstHead;    int i = m_uiLevel;    for (; i >= 0; --i)    {        while((q=p->next[i]) && q->key < key)        {            p = q;        }        update[i] = p;    }    if (!q || q->key != key)    {        return false;    }    for (i = m_uiLevel; i >= 0; --i)    {        if (update[i]->next[i] == q)        {            update[i]->next[i] = q->next[i];            if (m_pstHead->next[i] == NULL)            {                --m_uiLevel;            }        }    }    free(q);    q = NULL;    return true;}template<class KEY_TYPE, class VAL_TYPE>VAL_TYPE* CSkipList<KEY_TYPE, VAL_TYPE>::Search(KEY_TYPE key){    Node *q = NULL;    Node *p = m_pstHead;    int i = m_uiLevel;    for (; i >= 0; --i)    {        while((q=p->next[i]) && q->key < key)        {            p =q;        }        if (q && key == q->key)        {            return &(q->value);        }    }    return NULL;}template<class KEY_TYPE, class VAL_TYPE>inline CSkipList<KEY_TYPE,VAL_TYPE>::Iterator::Iterator(const CSkipList* list){    m_poList = list;    assert(list);    m_pstNode = list->m_pstHead;}template<class KEY_TYPE, class VAL_TYPE>inline const KEY_TYPE& CSkipList<KEY_TYPE, VAL_TYPE>::Iterator::Key() const{    assert(m_pstNode);    return m_pstNode->key;}template<class KEY_TYPE, class VAL_TYPE>inline VAL_TYPE* CSkipList<KEY_TYPE, VAL_TYPE>::Iterator::Value() const{    assert(m_pstNode);    return &(m_pstNode->value);}template<class KEY_TYPE, class VAL_TYPE>inline bool CSkipList<KEY_TYPE, VAL_TYPE>::Iterator::IsEnd() const{    return NULL == m_pstNode;}template<class KEY_TYPE, class VAL_TYPE>inline bool CSkipList<KEY_TYPE, VAL_TYPE>::Iterator::Next(){    if (NULL == m_pstNode || NULL == m_pstNode->next[0])    {        return false;    }    m_pstNode = m_pstNode->next[0];    return true;}int main(int argc, char *argv[]){    int iMaxLevel = 5;    int iEntry = 10;    CSkipList<int, int> sl(5);    srand(time(0));    cout << "test insert: " << sl.Insert(10 , 11) << endl;    cout << "test search: " << *(sl.Search(10)) << endl;    cout << "test erase: " << sl.Erase(10) << endl;    cout << "test search after erase: " << (sl.Search(10) ? "Found" : "Not Found")  << endl;    for (int i = 0; i < iEntry; ++i)    {        int e = rand() % iEntry;        cout << e << endl;        sl.Insert(e, e + 1);    }    CSkipList<int, int>::Iterator it(&sl);    while (it.Next())    {       cout << "key=" << it.Key() << ", value=" << *(it.Value()) << endl;    }    return 0;}

参考资料：
http://www.ezlippi.com/blog/2014/12/skip-list.html