哈希表分離鏈接法--兩種初始化方法及其對比

在教材中多爲第一種方法。實際上可以改變，減少h->tablesize次的malloc()操作

下面是依次是聲明、方法一、方法二：

typedef int ElementType;
/* hashSep.h */
#ifndef HashSep_H
#define HashSep_H
typedef unsigned int Index;						//Hash()散列函數的返回類型
struct listnode;
typedef struct listnode *position;
typedef struct listnode *list;
struct hashta1;
typedef struct hashta1 *hashtable;

list MakeEmpty(void);
hashtable InitTable_1(int tableSize);			//一個不太好的初始化程序
hashtable InitTable_2(int tableSize);			//一個比較好的初始化程序
void DestoryTable(hashtable h);
position Find(ElementType key, hashtable h);
void Insert(ElementType key, hashtable h);
ElementType Retrieve(position p);

#endif
/* ENDING */

/* hashSep.c */
	/* The list using headers */
#include<stdio.h>
#include<stdlib.h>
#define MinTableSize (5)
struct listnode
{
	ElementType element;
	position next;
};
struct hashta1
{
	int  tableSize;
	list *theLists;			//	指向指針的指針
};

hashtable InitTable_1(int tableSize)
{
	hashtable h;
	int i;

	if (tableSize < MinTableSize)
	{
		printf("Table size too small!!\n");
		return NULL;
	}

	/* allocate tabel */
	h = malloc(sizeof(struct hashta1));
	if (h == NULL)
	{
		printf("Out of space!!\n");
		exit(1);
	}
	h->tableSize =NextPrime(tableSize);

	/* allocate array of lists */
	h->theLists = malloc(sizeof(list)*h->tableSize);   
	//本方法中，存放的是多個headers指針，不是listnode結構體，故下面要有 h->tableSize次調用malloc函數爲數組中的每個指針賦值
	if(h->theLists==NULL)
	{ 
		printf("Out of space!!\n");
		exit(1);
	}

	/* allocate list header */
	for (i = 0;i < h->tableSize;++i)
	{
		h->theLists[i] = malloc(sizeof(struct listnode));
		if (h->theLists[i] == NULL)
		{
			printf("Out of space!!\n");
			exit(1);
		}
		else
			h->theLists[i]->next= NULL;
	}

	return h;
}

hashtable InitTable_2(int tableSize)
{
	hashtable h;
	int i;

	if (tableSize < MinTableSize)
	{
		printf("Table size too small!\n");
		return NULL;
	}

	/* allocate table */
	h = malloc(sizeof(struct hashta1));
	if (h == NULL)
	{
		printf("Out of space!!\n");
		exit(1);
	}
	h->tableSize = NextPrime(tableSize);

	/* allocate array of list */
	h->theLists = malloc(sizeof(struct listnode)*h->tableSize);   
	//避免了調用h->tableSize次的malloc()爲h->theLists[i]賦值,降低時間複雜度
	if (h->theLists == NULL)
	{
		printf("Out of space!!\n");
		exit(1);
	}

	/* allocate list header */
	for (i = 0;i < h->tableSize;++i)
	{
		h->theLists[i]->next= MakeEmpty();
	}
}