跳跃表的实现

最近看redis，又看到了跳跃表，不记得什么时候在哪里做题遇到过，忍不住自己写了一个跳跃表。下面是一些核心代码。

//// Created by ma on 2015/6/29.//#ifndef SKIPLIST_H_#define SKIPLIST_H_#include <stddef.h>#define MAX_LEVEL 16class Random{public:    static int randlevel();    static bool rand();private:    static long seeds;};class skiplistnode{public:    skiplistnode(int key=-1, int value=-1);    skiplistnode* &forward(const size_t& i);    int key()   { return _key;}    int value() { return _value;}    bool insert_after(skiplistnode* p,int i);    bool skip_after(int i);private:    int _key;    int _value;    int level;    skiplistnode *_forward[MAX_LEVEL];};class skiplist {public:    skiplist();    ~skiplist();    bool Insert(const int& key,const int& value);    bool Delete(const int& key);private:    int level;    skiplistnode *head;};#endif //SKIPLIST_H_

//// Created by ma on 2015/6/29.//#include <stdlib.h>#include <time.h>#include <assert.h>#include "skiplist.h"skiplistnode *&skiplistnode::forward(const size_t &i) {    return _forward[i];}skiplistnode::skiplistnode(int key, int value) : _key(key), _value(value), level(0) {    for (int i = 0; i < MAX_LEVEL; ++i) {        _forward[i] = NULL;    }}bool skiplistnode::insert_after(skiplistnode *p, int i) {    p->forward(i) = this->forward(i);    this->forward(i) = p;    return true;}bool skiplistnode::skip_after(int i) {    skiplistnode *p = this->forward(i);    assert (p != NULL);    this->forward(i) = p->forward(i);    return true;}skiplist::skiplist() : level(MAX_LEVEL) {    head = new skiplistnode();    for (int i = 0; i < MAX_LEVEL; ++i) {        head->forward(i) = NULL;    }}skiplist::~skiplist() {}bool skiplist::Insert(const int &key, const int &value) {    skiplistnode *nodes[MAX_LEVEL];    skiplistnode *q;    skiplistnode *p = head;    for (size_t i = level; i >= 0; i--) {        while ((q = p->forward(i)) && (q->key() < key))            p = q;        nodes[i] = p;    }    if (q && (q->key() == key))        return false;    int k = Random::randlevel();    skiplistnode *newnode = new skiplistnode(key, value);    for (int j = 0; j < k; ++j) {        nodes[j]->insert_after(newnode, j);    }    return true;}bool skiplist::Delete(const int &key) {    skiplistnode *q;    skiplistnode *p = head;    for (size_t i = level; i >= 0; i--) {        while ((q = p->forward(i)) && (q->key() < key))            p = q;        if (q && (q->key() == key)) {            p->skip_after(i);        }    }    if (q && (q->key() == key))        delete (q);    return true;}long Random::seeds = 0;bool Random::rand() {    srand(time(NULL) + seeds++);    return random() % 2;}int Random::randlevel() {    int level = 0;    while (rand())        level++;    level = level < MAX_LEVEL ? level : MAX_LEVEL;    return level;}