C 数据结构与算法 散列表

摘要: 哈希表

看到了关于 散列表 的一篇质量较高的博客（就不用自己写了，偷个懒）

http://www.nowamagic.net/academy/detail/3008010

这是一个系列的教程全部看完就差不多 有个概念了 但是还是不敢说 全懂

资质比较愚钝，木办法

下面的是实验代码 个人敲了一遍 理解了一些

//#include "stdafx.h"
#include "string.h"
#include "stdio.h"
#include "stdlib.h"

//data struct
typedef struct _node
{
char *name;         //key
char *desc;         //value
struct _node *next; //next node address
} node;

#define HASHSIZE 101   //define hashzize
static node* hashtab[HASHSIZE];

void inithashtab()
{
int i;
for(i=0; i < HASHSIZE; i++)
hashtab[i]=NULL;
}

unsigned int hash(char *s)
{
unsigned int h=0;
for(; *s; s++)
h=*s+h*31;
return h%HASHSIZE;
}

//look for the specific value
node* lookup(char *n)
{
unsigned int hi=hash(n);
node* np=hashtab[hi];
for(; np!=NULL; np=np->next)
{
if(!strcmp(np->name,n))
return np;
}

return NULL;
}

char* m_strdup(char *o)
{
int l=strlen(o)+1;
char *ns=(char*)malloc(l*sizeof(char));
strcpy(ns,o);
if(ns==NULL)
return NULL;
else
return ns;
}

char* get(char* name)
{
node* n=lookup(name);
if(n==NULL)
return NULL;
else
return n->desc;
}

//散列化 键 为对应的 数字 把萝卜放到对应的坑里面
int install(char* name,char* desc)
{
unsigned int hi;
node* np;
if((np=lookup(name))==NULL)
{
hi=hash(name);
np=(node*)malloc(sizeof(node));
if(np==NULL)
return 0;
np->name=m_strdup(name);
if(np->name==NULL) return 0;
np->next=hashtab[hi];
hashtab[hi]=np;
}
else
free(np->desc);
np->desc=m_strdup(desc);
if(np->desc==NULL) return 0;

return 1;
}

/* A pretty useless but good debugging function,
which simply displays the hashtable in (key.value) pairs
*/
void displaytable()
{
int i;
node *t;
for(i=0; i < HASHSIZE; i++)
{
if(hashtab[i]==NULL)
printf("()");
else
{
t=hashtab[i];
printf("(");
for(; t!=NULL; t=t->next)
printf("(%s.%s) ",t->name,t->desc);
printf(".)");
}
}
}

void cleanup()
{
int i;
node *np,*t;
for(i=0; i < HASHSIZE; i++)
{
if(hashtab[i]!=NULL)
{
np=hashtab[i];
while(np!=NULL)
{
t=np->next;
free(np->name);
free(np->desc);
free(np);
np=t;
}
}
}
}

main()
{
int i;
char* names[]= {"name","address","phone","k101","k110","nickname"};
char* descs[]= {"Sourav","Sinagor","26300788","Value1","Value2","ningjin"};

inithashtab();
for(i=0; i < 6; i++)
install(names[i],descs[i]);

printf("Done");
printf("If we didnt do anything wrong..""we should see %s\n",get("k110"));

install("phone","9433120451");

printf("Again if we go right, we have %s and %s",get("k101"),get("phone"));

printf("\nnickname:%s\n", get("nickname"));
/*displaytable();*/
cleanup();
return 0;
}