skip list

 

 

 

 

简单实现了建skip list的过程，至于查找，删除，有了参考文献[1]的算法，很容易实现的，这里就不赘述了。

 

#include <stdio.h>#include <stdlib.h>#include <assert.h>#include <time.h>#define INT_MIN ((int)(1 << 31))#define INT_MAX ((int)((unsigned int)(1 << 31) - 1))#define MAXLEVEL 10#define PROBABILITY 0.1#define DEBUGtypedef struct Node{int key;struct Node *next, *down;}Node;static Node NIL = {INT_MAX, NULL, NULL};static Node *head = NULL;static int skiplist_level = 0;static void skiplist_print(){int i;Node *node, *t = head;for(i = skiplist_level; i >= 0; i--){printf("%d: ", i);for (node = t; node; node = node->next){printf("%d ", node->key);}t = t->down;printf("/n");}}Node *new_node(int key, Node *next, Node *down){Node *node = (Node *)malloc(sizeof(Node));#if 0printf("%d/n", INT_MIN);#endifif (!node){printf("no mem to malloc/n");exit(1);}node->key = key;node->next = next;node->down = down;return node;}static inline float gen_p(){return (float)random() / RAND_MAX; //[0, 1]//return 0;}static int skiplist_randlevel(){int level = 0;while (gen_p() < PROBABILITY && level < MAXLEVEL - 1){level++;}return level;}static Node *skiplist_insert(int key){Node *update[MAXLEVEL];Node *node, *tmp;int level;int i;for (node = head, i = skiplist_level; i >= 0; i--){while (node->next->key < key){node = node->next;}/*node->key < key <= node->next->key*/update[i] = node;if (i){node = node->down;}}/*level 0*/node = node->next;/*insert*/if (1 /*node->key != key*/){level = skiplist_randlevel();if (level > skiplist_level){for (i = skiplist_level + 1; i <= level; i++){update[i] = new_node(INT_MIN, &NIL, head);head = update[i];}skiplist_level = level;}/*has got insertion place*/tmp = NULL;#ifdef DEBUGprintf("level: %d update: ", level);#endiffor (i = 0; i <= skiplist_level; i++){node = new_node(key, update[i]->next, tmp);update[i]->next = node;#ifdef DEBUGprintf("%d ", update[i]->key);#endiftmp = node;}#ifdef DEBUGprintf("/n");#endif}return head;}static Node *build_skiplist(FILE *file){int key;//build empty skiplisthead = new_node(INT_MIN, &NIL, NULL);skiplist_level = 0;while (EOF != fscanf(file, "%d", &key)){#ifdef DEBUGskiplist_print();printf("*********************/n");printf("%d/n", key);#endifskiplist_insert(key);}#ifdef DEBUGskiplist_print();printf("*********************/n");#endifreturn head;}static void foo(FILE *file){srandom((unsigned int)time(NULL));head = build_skiplist(file);//TODO}int main(int argc, char **argv){FILE *file;file = fopen("skiplist.input", "r");if (!file){perror("fopen"); exit(1);}foo(file);fclose(file);return 0;} 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

参考文献

[1] William Pugh. Skip lists: a probabilistic alternative to balanced trees. In Communications of the ACM. page 668-676, 1990.