C++实现的哈希搜索
C++实现的哈希搜索
程序内容
Complete a text searching engine using hash table.
完成一个文本搜索引擎，使用哈希表
程序设计
程序流程图
程序代码
程序变量
const int HASH_SIZE=100;
vector<string> container;
struct hash_node{
int number;
string key;
hash_node* next;
hash_node(string a="",int b=0,hash_node* c=NULL);
};
hash_node* hash_chain=NULL;
string word;
初始化
方法是从文件流单个读取字符，遇到句号，问号，感叹号和省略号都视为断句标志，利用了char和string之间的转换，出现bug的情况是句子字符长度超过1024，这个概率太小。程序兼顾了去除前导空格的功能。
bool ReadFile(string source){//读取文件并存储
ifstream fin;
fin.open(source.c_str());
if(!fin){//打开文件失败
cout<<"Unable to open "<<source<<"."<<endl;
return false;
}
//cout<<"open success"<<endl;
container.clear();
char buffer[1024]={0};
int k=0;
string temp;
while(!fin.eof()){
buffer[k++]=fin.get();
//断句符有三个
if(buffer[k-1]=='.'||buffer[k-1]=='?'||buffer[k-1]=='!'){
temp=buffer;
container.push_back(temp);
memset(buffer,0,1024);
k=0;
while(!fin.eof()){
if(isalpha(buffer[k]=fin.get())){
k=1;
break;
}
}
}
}
fin.close();
cout<<"succeed to open "<<source<<"."<<endl;
return true;
}
创建哈希表
核心哈希函数，string转int，来源CSDN博客独孤小剑，自己改进了取模操作
int Hash(string &key){//哈希 string转int
int seed=31;
int hash=0;
int strln=key.length();
for(int i=0;i<strln;i++)
hash=(hash*seed+key[i])%HASH_SIZE;
return hash%HASH_SIZE;
}
生成哈希表函数，从容器中逐个取出单词（消除最后一个单词的标点符号），根据哈希函数存储在哈希表中，利用自定义的结构体。同一个句子中相同的单词只存储一次。
void CreatHashTable(){//生成哈希表
hash_chain=new hash_node [HASH_SIZE];
for(int i=0;i<HASH_SIZE;i++){//初始化
hash_chain[i].key="";
hash_chain[i].number=0;
hash_chain[i].next=NULL;
}
int pos;
string temp;
for(int i=0;i<container.size();i++){
temp=container[i];//去除结尾符号
transform(temp.begin(),temp.end(),temp.begin(),Cut);
//cout<<container[i]<<endl;
istringstream iss(temp);
while(iss>>temp){//读取单词
//cout<<temp<<endl;
pos=Hash(temp);
hash_node* p1=&hash_chain[pos];
if(p1->key==""){
p1->key=temp;
p1->number=i;
}
else{
bool repeat=false;
while(p1->next!=NULL){
if(temp==p1->key&&i==p1->number){
repeat=true;
break;
}
p1=p1->next;
}
if(temp==p1->key&&i==p1->number){
repeat=true;
}
if(repeat)
continue;
hash_node* pnew=new hash_node(temp,i,NULL);
pnew->next=p1->next;
p1->next=pnew;
}
}
}
}
搜索关键词
前提是成功打开文件。利用循环多次搜索，退出的关键词是END（大小写敏感）。instruction（）函数中有说明退出方法。
int main()
{
instruction();
if(ReadFile("source.txt")){
//PrintContainer();
CreatHashTable();
cout<<"Please enter you key: ";
while((cin>>word)&&word!="END"){
SearchFor(word);
cout<<"Please enter you key: ";
}
DeleteHashTable();
}
return 0;
}
释放内存
良好习惯（强迫症罢了），据说这才是程序不崩溃的核心=。=
void DeleteHashTable(){//删除哈希表
hash_node *p1,*p2,*p3;
for(int i=0;i<HASH_SIZE;i++){
p1=&hash_chain[i];
p2=p1->next;
while(p2!=NULL){
p3=p2->next;
delete p2;
p2=p3;
}
}
delete [] hash_chain;
container.clear();
}
程序运行情况
完整代码
#include<bits/stdc++.h>
using namespace std;
const int HASH_SIZE=100;
vector<string> container;
struct hash_node{
int number;
string key;
hash_node* next;
hash_node(string a="",int b=0,hash_node* c=NULL);
};
hash_node* hash_chain=NULL;
string word;
bool ReadFile(string source);
void PrintContainer();
void CreatHashTable();
int Hash(string &key);
char Cut(char c);
void SearchFor(string word);
void instruction();
void DeleteHashTable();
int main()
{
instruction();
if(ReadFile("source.txt")){
//PrintContainer();
CreatHashTable();
cout<<"Please enter you key: ";
while((cin>>word)&&word!="END"){
SearchFor(word);
cout<<"Please enter you key: ";
}
DeleteHashTable();
}
return 0;
}
void instruction(){//程序介绍
cout<<"Programme: Search.cpp"<<endl;
cout<<"Author: Wsine"<<endl;
cout<<"Date: 2014-11-29"<<endl;
cout<<"Exit key is 'END'"<<endl<<endl;
}
bool ReadFile(string source){//读取文件并存储
ifstream fin;
fin.open(source.c_str());
if(!fin){//打开文件失败
cout<<"Unable to open "<<source<<"."<<endl;
return false;
}
//cout<<"open success"<<endl;
container.clear();
char buffer[1024]={0};
int k=0;
string temp;
while(!fin.eof()){
buffer[k++]=fin.get();
//断句符有三个
if(buffer[k-1]=='.'||buffer[k-1]=='?'||buffer[k-1]=='!'){
temp=buffer;
container.push_back(temp);
memset(buffer,0,1024);
k=0;
while(!fin.eof()){
if(isalpha(buffer[k]=fin.get())){
k=1;
break;
}
}
}
}
fin.close();
cout<<"succeed to open "<<source<<"."<<endl;
return true;
}
void PrintContainer(){//打印函数供测试使用
for(int i=0;i<container.size();i++)
cout<<container[i]<<endl;
}
int Hash(string &key){//哈希 string转int
int seed=31;
int hash=0;
int strln=key.length();
for(int i=0;i<strln;i++)
hash=(hash*seed+key[i])%HASH_SIZE;
return hash%HASH_SIZE;
}
char Cut(char c){//自定义切割函数
if(isalpha(c)||c=='\0')
return c;
else
return ' ';
}
void CreatHashTable(){//生成哈希表
hash_chain=new hash_node [HASH_SIZE];
for(int i=0;i<HASH_SIZE;i++){//初始化
hash_chain[i].key="";
hash_chain[i].number=0;
hash_chain[i].next=NULL;
}
int pos;
string temp;
for(int i=0;i<container.size();i++){
temp=container[i];//去除结尾符号
transform(temp.begin(),temp.end(),temp.begin(),Cut);
//cout<<container[i]<<endl;
istringstream iss(temp);
while(iss>>temp){//读取单词
//cout<<temp<<endl;
pos=Hash(temp);
hash_node* p1=&hash_chain[pos];
if(p1->key==""){
p1->key=temp;
p1->number=i;
}
else{
bool repeat=false;
while(p1->next!=NULL){
if(temp==p1->key&&i==p1->number){
repeat=true;
break;
}
p1=p1->next;
}
if(temp==p1->key&&i==p1->number){
repeat=true;
}
if(repeat)
continue;
hash_node* pnew=new hash_node(temp,i,NULL);
pnew->next=p1->next;
p1->next=pnew;
}
}
}
}
hash_node::hash_node(string a,int b,hash_node* c){//结构体构造函数
key=a;
number=b;
next=c;
}
void SearchFor(string word){//搜索函数
int pos=Hash(word),k=1;
hash_node* p1=&hash_chain[pos];
while(p1!=NULL){//遍历链表
if(p1->key==word){
cout<<endl;
cout<<"Sentence "<<k++<<" :"<<endl;
cout<<container[p1->number]<<endl;
}
p1=p1->next;
}
cout<<endl;
}
void DeleteHashTable(){//删除哈希表
hash_node *p1,*p2,*p3;
for(int i=0;i<HASH_SIZE;i++){
p1=&hash_chain[i];
p2=p1->next;
while(p2!=NULL){
p3=p2->next;
delete p2;
p2=p3;
}
}
delete [] hash_chain;
container.clear();
}
