hash表

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StringHash.h

 #include <StdAfx.h>  #include <string>   using namespace std;    #pragma once   #define MAXTABLELEN 1024    // 默认哈希索引表大小  //////////////////////////////////////////////////////////////////////////   // 哈希索引表定义   typedef struct  _HASHTABLE {       long nHashA;       long nHashB;       bool bExists;   }HASHTABLE, *PHASHTABLE ;  class StringHash { public:    StringHash(const long nTableLength = MAXTABLELEN);     ~StringHash(void); private:       unsigned long cryptTable[0x500];     unsigned long m_tablelength;    // 哈希索引表长度      HASHTABLE *m_HashIndexTable;  private:    void InitCryptTable();                                               // 对哈希索引表预处理     unsigned long HashString(const string &lpszString, unsigned long dwHashType); // 求取哈希值       public:    bool Hash(string url);    unsigned long Hashed(string url);    // 检测url是否被hash过};

StringHash.cpp

#include "StdAfx.h"#include "StringHash.h"StringHash::StringHash(const long nTableLength /*= MAXTABLELEN*/){    InitCryptTable();      m_tablelength = nTableLength;      //初始化hash表    m_HashIndexTable = new HASHTABLE[nTableLength];      for ( int i = 0; i < nTableLength; i++ )      {          m_HashIndexTable[i].nHashA = -1;          m_HashIndexTable[i].nHashB = -1;          m_HashIndexTable[i].bExists = false;      }          }StringHash::~StringHash(void){    //清理内存    if ( NULL != m_HashIndexTable )      {          delete []m_HashIndexTable;          m_HashIndexTable = NULL;          m_tablelength = 0;      }  }/************************************************************************//*函数名：InitCryptTable/*功  能：对哈希索引表预处理  /*返回值：无/************************************************************************/void StringHash::InitCryptTable()  {       unsigned long seed = 0x00100001, index1 = 0, index2 = 0, i;      for( index1 = 0; index1 < 0x100; index1++ )      {           for( index2 = index1, i = 0; i < 5; i++, index2 += 0x100 )          {               unsigned long temp1, temp2;              seed = (seed * 125 + 3) % 0x2AAAAB;              temp1 = (seed & 0xFFFF) << 0x10;              seed = (seed * 125 + 3) % 0x2AAAAB;              temp2 = (seed & 0xFFFF);              cryptTable[index2] = ( temp1 | temp2 );           }       }   }  /************************************************************************//*函数名：HashString/*功  能：求取哈希值   /*返回值：返回hash值/************************************************************************/unsigned long StringHash::HashString(const string& lpszString, unsigned long dwHashType)  {       unsigned char *key = (unsigned char *)(const_cast<char*>(lpszString.c_str()));      unsigned long seed1 = 0x7FED7FED, seed2 = 0xEEEEEEEE;      int ch;      while(*key != 0)      {           ch = toupper(*key++);          seed1 = cryptTable[(dwHashType << 8) + ch] ^ (seed1 + seed2);          seed2 = ch + seed1 + seed2 + (seed2 << 5) + 3;       }      return seed1;   }  /************************************************************************//*函数名：Hashed/*功  能：检测一个字符串是否被hash过/*返回值：如果存在，返回位置；否则，返回-1/************************************************************************/unsigned long StringHash::Hashed(string lpszString)  {       const unsigned long HASH_OFFSET = 0, HASH_A = 1, HASH_B = 2;      //不同的字符串三次hash还会碰撞的几率无限接近于不可能    unsigned long nHash = HashString(lpszString, HASH_OFFSET);      unsigned long nHashA = HashString(lpszString, HASH_A);      unsigned long nHashB = HashString(lpszString, HASH_B);      unsigned long nHashStart = nHash % m_tablelength,      nHashPos = nHashStart;      while ( m_HashIndexTable[nHashPos].bExists)      {           if (m_HashIndexTable[nHashPos].nHashA == nHashA && m_HashIndexTable[nHashPos].nHashB == nHashB)               return nHashPos;           else               nHashPos = (nHashPos + 1) % m_tablelength;          if (nHashPos == nHashStart)               break;       }      return -1; //没有找到  }  /************************************************************************//*函数名：Hash/*功  能：hash一个字符串 /*返回值：成功，返回true；失败，返回false/************************************************************************/bool StringHash::Hash(string lpszString){      const unsigned long HASH_OFFSET = 0, HASH_A = 1, HASH_B = 2;      unsigned long nHash = HashString(lpszString, HASH_OFFSET);      unsigned long nHashA = HashString(lpszString, HASH_A);      unsigned long nHashB = HashString(lpszString, HASH_B);      unsigned long nHashStart = nHash % m_tablelength,         nHashPos = nHashStart;      while ( m_HashIndexTable[nHashPos].bExists)      {           nHashPos = (nHashPos + 1) % m_tablelength;          if (nHashPos == nHashStart) //一个轮回          {              //hash表中没有空余的位置了,无法完成hash            return false;           }      }      m_HashIndexTable[nHashPos].bExists = true;      m_HashIndexTable[nHashPos].nHashA = nHashA;      m_HashIndexTable[nHashPos].nHashB = nHashB;      return true;  }

原文地址：http://www.cnblogs.com/xiekeli/archive/2012/01/17/2324433.html

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