/*
* hashquad.c 开放定址法解决hash冲突问题
*/
#include
#include
#include "hashquad.h"
#include "fatal.h"
#define MIN_TABLE_SIZE (10)
#define REHASH_FACTOR (0.7)
enum kind_of_entry { legitimate, empty, deleted };
struct hash_entry
{
element_type element;
enum kind_of_entry info;
};
typedef struct hash_entry cell;
struct hash_tbl
{
int table_size; /* 表容量 */
int entry_cnt; /* 已填入的单元数量 */
cell *cells;
};
static int
need_rehash( hash_table h )
{
return ( h->entry_cnt > h->table_size * REHASH_FACTOR );
}
static int
next_prime( int N )
{
int i;
if ( N % 2 == 0 )
N++;
for ( ; ; N += 2 ){
for ( i = 3; i * i <= N; i += 2 ){
if ( N % i == 0 )
goto cont_outer;
}
return N;
cont_outer: ;
}
}
static Index
hash( element_type key, int table_size )
{
return key % table_size;
}
static hash_table
initialize_table( int table_size )
{
hash_table h;
int i;
if ( table_size < MIN_TABLE_SIZE )
Error("Table size too small!");
h = malloc( sizeof( struct hash_tbl ) );
if ( h == NULL )
Error("Out of space!");
h->table_size = next_prime( table_size );
h->cells = malloc( sizeof( cell ) * h->table_size );
if ( h->cells == NULL ){
free( h );
Error("Out of space!");
}
for ( i = 0; i < h->table_size; i++){
h->cells[ i ].info = empty;
}
h->entry_cnt = 0;
return h;
}
static Pos
find( element_type key, hash_table h )
{
Pos cur_pos;
int collision_num;
collision_num = 0;
cur_pos = hash( key, h->table_size );
/*
当hash表大部分被占满,这个过程可能很慢。
也有可能进入死循环! 需要在适当的时候进行rehash!
*/
while ( h->cells[ cur_pos ].info != empty
&& h->cells[ cur_pos ].element != key ){
cur_pos += 2 * ++collision_num - 1;
if ( cur_pos >= h->table_size )
cur_pos -= h->table_size;
}
return cur_pos;
}
static void
insert( element_type key, hash_table h )
{
Pos p;
p = find( key, h );
if ( h->cells[ p ].info != legitimate ){
h->cells[ p ].info = legitimate;
h->cells[ p ].element = key;
h->entry_cnt++;
}
}
static hash_table
rehash( hash_table h)
{
int i, old_size;
cell *old_cells;
old_cells = h->cells;
old_size = h->table_size;
/* 创建一个新的double size的空表 */
h = initialize_table( 2 * old_size );
/* 拷贝旧表的数据到新表 */
for ( i = 0; i < old_size; i++ ){
if ( old_cells[ i ].info == legitimate )
insert( old_cells[ i ].element, h );
}
free( old_cells );
return h;
}
/************ The next is test functions ***************/
#define get_array_size(array) ( sizeof(array) / sizeof(array[0]) )
void
test_hashquad( void )
{
int i;
Pos p;
hash_table h;
element_type datas[100];
for ( i = 0; i < get_array_size( datas ); i++ ){
datas[i] = rand() % 1000;
}
h = initialize_table( 13 );
if ( h == NULL )
Error("Initialize error!");
for ( i = 0; i < get_array_size( datas ); i++ ){
insert( datas[i], h );
/* 在每次插入操作后检查是否需要rehash */
if ( need_rehash( h ) )
h = rehash( h );
}
p = find( 67, h );
if ( h->cells[p].info != legitimate ){
printf("\n\t key value 67 not in hash table!\n");
}else{
printf("\n\t key value 67 in hash table!\n");
}
p = find( datas[31], h );
if ( h->cells[p].info != legitimate ){
printf("\n\t key value %d not in hash table!\n",datas[31]);
}else{
printf("\n\t key value %d in hash table!\n",datas[31]);
}
i = i;
return;
}
/*********************************************************************************************************/
/* hashquad.h */
#ifndef _HASHQUAD_H_
#define _HASHQUAD_H_
typedef int element_type;
typedef unsigned int Index;
typedef Index Pos;
struct hash_tbl;
typedef struct hash_tbl *hash_table;
#endif
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