simple skiplist implementation in c

最新推荐文章于 2021-08-07 17:05:49 发布

原创最新推荐文章于 2021-08-07 17:05:49 发布 · 924 阅读

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本文详细介绍了跳表的数据结构设计、初始化、删除、添加、查找、释放等核心操作的实现过程，通过实例代码展示跳表的高效性和灵活性。

#ifndef MY_SKIP_LIST
#define MY_SKIP_LIST

#include <stdlib.h>
#include <stdio.h>
#include <limits.h>

typedef int DataType;

#define MAX_LEVEL 8

struct DataNode;


typedef struct NodeLevel
{
    struct DataNode * forward;
    unsigned span;

}NodeLevel,*PNodeLevel;

/**
data node which stores data with DataType
*/
typedef struct DataNode
{
//    int (*compare)(DataType val1,DataType val2);
    DataType value;
    unsigned level_size;
    NodeLevel level[];

}DataNode,*PDataNode;


/**
skip list struct
*/
typedef struct SkipList
{
    unsigned level;
    unsigned size;
    PDataNode header;

}SkipList,*PSkipList;

/**
 *get rand level for data node created
 */
unsigned rand_level();

/**
 *initialize an empty skiplist
 */
PSkipList skiplist_init();

/**
 *destory a skip list 'sl',and free the memory occupied.
 */
void destory_skiplist(PSkipList *sl);

/**
 *make a new skip list node which stores 'val',
 *returns a pointer to the data node newly made
 */
PDataNode make_node(DataType val,unsigned level);

/**
 *delete a data node with data 'val' from skip list 'sl',
 *returns a pointer of DataNode deleted,
 *if DataNode with data 'val' does not exist,return NULL
 *note:memory occupied by 'val' not freed
 */
PDataNode del(PSkipList sl,DataType val);

/**
 *add a data node with data 'val' from skip list 'sl',
 *returns a pointer of DataNode added,
 *note:memory occupied by 'val' not freed
 */
PDataNode add(PSkipList sl,DataType val);

/**
 *find 'val' in skiplist 'sl',if founed,return the pointer of node with value 'val'
 *if not return NULL
 */
PDataNode find(PSkipList sl,DataType val);

/**
 *free the memory occupied by 'node'
 */
void free_node(PDataNode node);

void print_skiplist(PSkipList sl);
void print_level(PSkipList sl, int i);

#endif // MY_SKIP_LIST

#include "skiplist.h"

unsigned rand_level()
{
    int level = 1;
    while(rand()%2 && level <= MAX_LEVEL)
        level++;
    return level;
}

PDataNode make_node(DataType val,unsigned level)
{
    PDataNode node = (PDataNode)malloc(sizeof(DataNode) + sizeof(NodeLevel)*level);
    if(node == NULL)
        return NULL;

    node->value = val;
    node->level_size = level;

    int i = 0;
    for(i=0; i<level; i++)
    {
        node->level[i].forward = NULL;
        node->level[i].span = 0;
    }
    return node;
}

void free_node(PDataNode node)
{
    if(NULL == node)
        return;
    free(node);
}

PSkipList skiplist_init()
{
    PSkipList sl = NULL;
    sl = (PSkipList)malloc(sizeof(SkipList));
    sl->level = 1;
    sl->size = 0;
    PDataNode header = make_node(INT_MIN,MAX_LEVEL);
    if(header == NULL)
    {
        free(sl);
        return NULL;
    }
    sl->header = header;
    return sl;
}
void destory_skiplist(PSkipList *sl)
{
    if(*sl == NULL) return;

    PDataNode pNode = (*sl)->header->level[0].forward;
    PDataNode next = NULL;
    while(pNode)
    {
        next = pNode->level[0].forward;
        free_node(pNode);
        pNode = next;
    }
    pNode = NULL;
    next = NULL;
    free_node((*sl)->header);
    (*sl)->header = NULL;
    free(*sl);
    (*sl) = NULL;
    return;
}

PDataNode del(PSkipList sl,DataType val)
{
    if(sl == NULL) return NULL;
    PDataNode del_node = NULL;
    PNodeLevel update[MAX_LEVEL];
    int i = MAX_LEVEL - 1;
    PDataNode cur,pre;
    pre = sl->header;
    cur = pre;
    while(i >= 0)
    {
        cur = pre->level[i].forward;
        while(cur != NULL && cur->value < val)
        {
            pre = cur;
            cur = cur->level[i].forward;
        }
        if(cur != NULL && cur->value == val)
        {
            del_node = cur;
        }
        update[i] = &(pre->level[i]);
        i--;
    }

    if(del_node == NULL)
        return NULL;

    i = MAX_LEVEL - 1;
    while(i >= 0)
    {
        if(update[i]->forward == NULL)
        {
            i--;
            continue;
        }
        else if(update[i]->forward->value > val)
        {
            update[i]->span--;
            i--;
        }
        else
        {
            update[i]->forward = del_node->level[i].forward;
            if(del_node->level[i].forward == NULL)
                update[i]->span = 0;
            else
                update[i]->span += del_node->level[i].span - 1;
            i--;
        }
    }
    sl->size--;
    return del_node;
}

PDataNode add(PSkipList sl,DataType val)
{
    if(sl == NULL) return NULL;
    unsigned node_level = rand_level();
    PDataNode pNode = make_node(val,node_level);
    printf("Level:%d   value:%d\n",node_level,val);
    if(pNode == NULL) return NULL;

    PNodeLevel update[MAX_LEVEL];
    //查找插入位置的遍历路径上处于第i层的节点在链表中的排位，头节点为rank[MAX_LEVEL-1]=0
    //查找从最高层开始且头节点在链表中是第一个，所以rank[MAX_LEVEL-1]=0
    unsigned rank[MAX_LEVEL] = {0};
    int i =  MAX_LEVEL-1;
    PDataNode cur,pre;
    pre = sl->header;
    cur = pre;
    while(i >= 0)
    {
        rank[i] = (i == MAX_LEVEL-1 ? 0 : rank[i+1]);
        cur = pre->level[i].forward;
        while(cur && cur->value < val)
        {
            rank[i] += pre->level[i].span;
            pre = cur;
            cur = cur->level[i].forward;
        }
        if(cur && cur->value == val)
            return NULL;
        update[i] = &(pre->level[i]);
        i--;
    }
    i = MAX_LEVEL-1;
    for(;i >=0; i--)
    {
        if(update[i]->forward == NULL && i > node_level-1)
        {
            continue;
        }
        else if(update[i]->forward == NULL && i <= node_level-1)
        {
            update[i]->forward = pNode;
            //节点的插入位置一定是在查找路基上第0层节点的后面一个
            //rank[0] - rank[i]得到的是查找路径上要更新的第层节点距离第0层节点的距离跨度，
            //这个跨度+1就得到了更新路劲上第i层节点到插入节点的跨度
            update[i]->span = (rank[0] - rank[i]) + 1;
        }
        else if(update[i]->forward && i > node_level-1)
        {
            update[i]->span++;
        }
        else
        {
            pNode->level[i].forward = update[i]->forward;
            //pNode->level[i].span = (update[i]->span + 1) - ((rank[0] - rank[i]) + 1);
            pNode->level[i].span = update[i]->span - (rank[0] - rank[i]);
            update[i]->forward = pNode;
            update[i]->span = (rank[0] - rank[i]) + 1;
        }
    }
    sl->size++;
    return pNode;
}

PDataNode find(PSkipList sl,DataType val)
{
    if(sl == NULL) return NULL;
    PDataNode pre  = sl->header;
    PDataNode cur = pre;
    int i =  MAX_LEVEL-1;
    unsigned rank[MAX_LEVEL-1] = {0};
    while(i >= 0)
    {
        rank[i] = (i == MAX_LEVEL-1 ? 0 : rank[i+1]);
        cur = pre->level[i].forward;
        while(cur != NULL && cur->value < val)
        {
            rank[i] += pre->level[i].span;
            pre = cur;
            cur = cur->level[i].forward;
        }
        if(cur != NULL && cur->value == val)
        {
            printf("val=%d,rank:%u\n",val,rank[i]+1);
            return cur;
        }
        i--;
    }
    return NULL;
}

void print_level(PSkipList sl, int i)
{
    PDataNode pNode = sl->header;
    printf("level  %d    ",i);
    while(pNode)
    {
        printf("%d",pNode->value);
        int num = pNode->level[i].span;
        while(num > 0)
        {
            printf("-");
            num--;
        }
        pNode = pNode->level[i].forward;
    }
    printf("\n");
}

void print_skiplist(PSkipList sl)
{
    if(sl == NULL)
    {
        printf("Null list");
        return ;
    }
    int i = MAX_LEVEL - 1;
    while(i >= 0)
    {
        print_level(sl,i);
        i--;
    }
}

#include <stdio.h>
#include <stdlib.h>
#include "skiplist.h"
int main()
{
    PSkipList sl = skiplist_init();
    DataType vals[] = {1,3,5,7,9,2,4,6,8,10,11,15,12,18,21,31,56,100,94,68,60,88,66};
    unsigned val_size = sizeof(vals)/sizeof(vals[0]);
    printf("value number = %u\n",val_size);
    unsigned i = 0;
    for(;i < val_size; i++)
    {
        add(sl,vals[i]);
    }
    print_skiplist(sl);
    find(sl,31);
    find(sl,100);
    find(sl,66);

    PDataNode del_node = del(sl,31);
    free_node(del_node);
    print_skiplist(sl);

    del_node = del(sl,88);
    free_node(del_node);
    print_skiplist(sl);

    del_node = del(sl,21);
    free_node(del_node);
    print_skiplist(sl);

    del_node = del(sl,6);
    free_node(del_node);
    print_skiplist(sl);

    del_node = del(sl,94);
    free_node(del_node);
    print_skiplist(sl);

    del_node = del(sl,60);
    free_node(del_node);
    print_skiplist(sl);

    del_node = del(sl,68);
    free_node(del_node);
    print_skiplist(sl);

    del_node = del(sl,100);
    free_node(del_node);
    print_skiplist(sl);

    del_node = del(sl,1);
    free_node(del_node);
    print_skiplist(sl);

    del_node = NULL;

    destory_skiplist(&sl);
    print_skiplist(sl);

    return 0;
}