哈希表，也叫散列表，是根据关键码值(Key　value)而直接进行访问的数据结构。也就是说，它通过把关键码值映射到表中一个位置来访问记录，以加快查找的速度。这个映射函数叫做哈希函数，存放记录的数组叫做哈希表。

哈希函数最主要的设计在于哈希函数和冲突处理的解决，其中哈希函数的设计方法主要有直接定址法和除留余数法；冲突处理的方法主要有开放定址法和链地址法。本文主要实现了一个基本存放字符串的哈希表，冲突处理采用链地址法。

代码如下：

#include <iostream>
#include<cstring>

#define HASHSIZE 19

using namespace std;

struct hashnode{
    char *key;
    char *value;
    hashnode *next;
};


char *strcopy(char *s)
{
    int len=strlen(s)+1;
    char *res=new char[len];
    strcpy(res,s);
    if(res==NULL)
        return NULL;
    return res;
}


class hashtable
{
public:
    hashtable();
    ~hashtable();
    unsigned int hasher(char *s);
    hashnode *hashfind(char *keys);
    bool hashinsert(char *keys,char *values);
    bool hashdelete(char *keys);
    void display();
private:
    hashnode *hashdata[HASHSIZE];
};

hashtable::hashtable()
{
    for(int i=0;i<HASHSIZE;i++)
        hashdata[i]=NULL;
}

hashtable::~hashtable()
{
    hashnode *p,*q;
    for(int i=0;i<HASHSIZE;i++)
    {
        if(hashdata[i]!=NULL)
        {
            p=hashdata[i];
            while(p)
            {
                q=p->next;
                delete p->key;
                delete p->value;
                delete p;
                p=q;
            }
        }
    }

}

//hash函数可以自己定义
unsigned int hashtable::hasher(char *s)
{
    unsigned int res=0;
    for(;*s!=‘\0‘;++s)
        res=*s+res;
    return res%HASHSIZE;
}

hashnode* hashtable::hashfind(char *keys)
{
    unsigned int res=hasher(keys);
    hashnode *p=hashdata[res];
    for(;p!=NULL;p=p->next)
        if(strcmp(p->key,keys)==0)
            return p;
    return NULL;
}

bool hashtable::hashinsert(char *keys,char *values)
{
    unsigned int res;
    if(keys==NULL)
        return 0;
    hashnode *p;
    if((p=hashfind(keys))==NULL)
    {
        res=hasher(keys);
        p=new hashnode;
        if(p==NULL)
            return 0;
        p->key=strcopy(keys);
        p->value=strcopy(values);
        if(p->key==NULL)
            return 0;

        p->next=hashdata[res];  //链表头插入
        hashdata[res]=p;
    }
    else
    {
        delete p->value;  //如果key在哈希表中，先删除原有value值
        p->value=strcopy(values);
    }
    if(p->value==NULL)
        return 0;
    return 1;
}

bool hashtable::hashdelete(char *keys)
{
    hashnode *p=NULL,*q=NULL;
    unsigned int res=hasher(keys);
    p=hashdata[res];
    if(!p)
        return 0;
    if(strcmp(p->key,keys)==0)
     {
         hashdata[res]=p->next;
         delete p->key;
         delete p->value;
         delete p;
     }
    q=p;p=q->next;
    while(p&&(strcmp(p->key,keys)!=0))
    {
        q=p;
        p=p->next;
    }
    if(p)
    {
        q->next=p->next;
        delete p->key;
        delete p->value;
        delete p;
    }
    return 1;
}

void hashtable::display()
{
    hashnode *p;
    for(int i=0;i<HASHSIZE;i++)
    {
        if(hashdata[i]==NULL)
            cout<<"()"<<endl;
        else
        {
            p=hashdata[i];
            cout<<"(";
            for(;p!=NULL;p=p->next)
                cout<<"("<<p->key<<","<<p->value<<")";
            cout<<")"<<endl;
        }
    }
}


int main()
{
    hashtable hash_table;
    hashnode *flag=NULL;
    char* keys[]= {"user1","user5","user13","user108","suer31","ersu13","user108"};
    char* values[]= {"mike","joy","hello","world","someone","15646","newworld"};

    for(int i=0;i<7;i++)
        hash_table.hashinsert(keys[i],values[i]);
    cout<<"The result is:"<<endl;
    hash_table.display();
    cout<<endl;
    flag=hash_table.hashfind("user108");
    if(flag==NULL)
        cout<<"the user is not found!"<<endl;
    else
        cout<<"the value is:"<<flag->value<<endl;
    hash_table.hashdelete("suer31");
    cout<<endl;
    cout<<"The new result is:"<<endl;
    hash_table.display();

    return 0;
}

C++链地址法实现哈希表,布布扣,bubuko.com

C++链地址法实现哈希表