算法学习-哈希表-白红宇

算法学习-哈希表

阅读量：4687 次

发布时间：2019-06-09

本文共 9264 字，大约阅读时间需要 30 分钟。

之前在大学学习数据结构的时候，学过数组和链表。数组的优点就是可以直接定位，速度快，但是缺点就是插入删除，效率就慢了很多。链表的可以快速的插入删除，但是不能直接定位，需要遍历才可以。他们使用在不同的场景下面。

有时候，又想快速的插入，又想快速的定位怎么办？这就需要把这两者优点糅合起来，哈希表就这么产生了。

哈希表的原理：一个动态数组，保存着元素的地址。通过一个公式，把元素的key（唯一），算出一个数值index。数组index位置就保存这个元素的指针。

这样存数据以及取数据，都可以通过这个公式，得到同一个位置。这个公式的目的，就是将key和数组的位置映射起来，当然没有任何的一个公式能够保证算出来的key和数组位置是一一对应的，也就是说，多个key算出来的index结果是同一个，这就是哈希冲突，稍后具体怎么解决它。

整个哈希表，最重要的就是这个映射公式，不但能够将字符串变成数值，而且能够平均分布。最常用的就是Times33算法

inline UINT CMyMap::HashKey(LPCTSTR key) const{UINT nHash = 5381;while (*key)nHash = (nHash << 5) + nHash + *key++;return nHash;}

5381是一个经验值，php就是使用这个值。

下面就是我写的代码。

1 #pragma once  2 #include "Bucket.h"  3 class HashTable  4 {  5 public:  6     HashTable(void);  7     ~HashTable(void);  8     static unsigned long hash_inline(const char* arKey,unsigned int nKeyLength);  9     bool add(const char* arKey,void* value); 10     void* getData(const char* arKey); 11     bool remove(const char* arKey); 12     bool resize(unsigned int nSize); 13     unsigned int nTableSize; 14     unsigned int nTableMask; 15     unsigned int nNumOfElements; 16     Bucket *pBucketCursor; 17     Bucket **arBuckets; 18     Bucket *pListHead; 19     Bucket *pListTail; 20 private: 21     void init(); 22 }; 23 #include "stdafx.h" 24 #include "HashTable.h" 25 #include 
      
        26 #include 
       
         27 using namespace std; 28 typedef unsigned long ulong; 29 typedef unsigned int uint; 30  31 HashTable::HashTable(void) 32 { 33     init(); 34 } 35  36 HashTable::~HashTable(void) 37 { 38     delete [] arBuckets; 39 } 40  41 ulong HashTable::hash_inline( const char* arKey,uint nKeyLength ) 42 { 43     register ulong hash=5381; 44 //     for (; nKeyLength >= 8; nKeyLength -= 8) 45 //     { 46 //         const char *arKeyTemp=arKey; 47 //         for(int i=0;i!=8;++i){ 48 //             hash = ((hash << 5) + hash) + *arKey++; 49 //             if(*arKey){ 50 //                 arKey=arKeyTemp; 51 //             } 52 //         }     53 //  54 //     } 55 //     switch (nKeyLength)  56 //     { 57 //         case 7: hash = ((hash << 5) + hash) + *arKey++; /* fallthrough... */ 58 //         case 6: hash = ((hash << 5) + hash) + *arKey++; /* fallthrough... */ 59 //         case 5: hash = ((hash << 5) + hash) + *arKey++; /* fallthrough... */ 60 //         case 4: hash = ((hash << 5) + hash) + *arKey++; /* fallthrough... */ 61 //         case 3: hash = ((hash << 5) + hash) + *arKey++; /* fallthrough... */ 62 //         case 2: hash = ((hash << 5) + hash) + *arKey++; /* fallthrough... */ 63 //         case 1: hash = ((hash << 5) + hash) + *arKey++; break; 64 //         case 0: break; 65 //     } 66     while (*arKey) 67     { 68         hash=(hash<<5)+hash+*arKey++; 69     } 70     return hash; 71 } 72  73 void HashTable::init() 74 { 75     nTableSize=8; 76     nTableMask=nTableSize-1; 77     arBuckets=new Bucket*[nTableSize](); 78     nNumOfElements=0; 79 } 80  81 bool HashTable::add(const char* arKey,void* value ) 82 { 83     ulong h=hash_inline(arKey,nTableSize); 84     uint nIndex=nTableMask&h; 85     Bucket *pbucket=arBuckets[nIndex]; 86     if (pbucket==NULL) 87     { 88         pbucket=new Bucket(arKey,value,h); 89         arBuckets[nIndex]=pbucket; 90         ++nNumOfElements; 91         if(nNumOfElements==1) 92         { 93             pListHead=pbucket; 94             pListTail=pbucket; 95         }else{ 96             pbucket->pListPre=pListTail; 97             pListTail->pListNext=pbucket; 98             pListTail=pbucket; 99         }100         //cout<<"add key "<
        
         arKey<
         
          arKey,arKey)==0){103             //cout<<"key "<
          
           <<" is existed"<
           
            pNext!=NULL)108 {109 pbucket=pbucket->pNext;110 }111 pbucket->pNext=pNewBucket;112 pNewBucket->pPre=pbucket;113 pNewBucket->pListPre=pListTail;114 pListTail->pListNext=pNewBucket;115 pListTail=pNewBucket;116 //cout<<"key "<
            
             arKey<<" next key is "<
             
              arKey<
              
               =nTableSize){121 resize(nTableSize*2);122 }123 return true;124 }125 126 bool HashTable::resize( unsigned int nSize )127 {128 Bucket **arPBucketTemp=new Bucket*[nSize]();129 Bucket *pListHeadTemp=NULL;130 Bucket *pListTailTemp=NULL;131 nTableSize=nSize;132 nTableMask=nTableSize-1;133 Bucket *pBucketCursorTemp=pListHead;134 uint nNumOfElementsTemp=0;135 //cout<<"--------------rehash-----------------"<
               
                arKey<
                
                 pListNext;142 ulong h=hash_inline(pbucket->arKey,nTableSize);143 pbucket->nKeyLength=nTableSize;144 pbucket->h=h;145 uint nIndex=h&nTableMask;146 Bucket *pbucketindex=arPBucketTemp[nIndex];147 if (pbucketindex==NULL)148 { 149 arPBucketTemp[nIndex]=pbucket;150 ++nNumOfElementsTemp;151 if(nNumOfElementsTemp==1)152 {153 pListHeadTemp=pbucket;154 pListTailTemp=pbucket;155 pbucket->pListPre=NULL;156 pbucket->pListNext=NULL;157 pbucket->pNext=NULL;158 pbucket->pPre=NULL;159 }else{160 pbucket->pListPre=pListTailTemp;161 pbucket->pListNext=NULL;162 pbucket->pPre=NULL;163 pbucket->pNext=NULL;164 pListTailTemp->pListNext=pbucket;165 pListTailTemp=pbucket;166 }167 }else{168 if(strcmp(pbucket->arKey,pbucketindex->arKey)==0){169 //cout<<"key "<
                 
                  arKey<<" is existed"<
                  
                   pNext!=NULL)173 {174 pbucketindex=pbucketindex->pNext;175 }176 pbucketindex->pNext=pbucket;177 pbucket->pPre=pbucketindex;178 pbucket->pNext=NULL;179 pbucket->pListPre=pListTailTemp;180 pbucket->pListNext=NULL;181 pListTailTemp->pListNext=pbucket;182 pListTailTemp=pbucket;183 /*//cout<<"key "<
                   
                    arKey<<" next key is "<
                    
                     pNext->arKey<
                     
                      arKey,arKey)==0){209 return pbucket->pData;210 }else{211 pbucket=pbucket->pNext;212 }213 }214 return NULL;215 }216 }217 218 bool HashTable::remove( const char* arKey )219 {220 ulong h=hash_inline(arKey,nTableSize);221 ulong nIndex=h&nTableMask;222 Bucket *pbucket=arBuckets[nIndex];223 if(pbucket==NULL){224 return false;225 }else{226 while (pbucket!=NULL)227 {228 if(strcmp(pbucket->arKey,arKey)==0){229 if(pbucket==pListHead){230 pListHead=pbucket->pListNext;231 if(pListHead!=NULL){232 pbucket->pListNext->pListPre=NULL;233 }234 }235 if(pbucket==pListTail){236 pListTail=pbucket->pListPre;237 if(pListTail!=NULL){238 pListTail->pListNext=NULL;239 }240 }241 if(pbucket->pListPre!=NULL){242 pbucket->pListPre->pListNext=pbucket->pListNext;243 }244 if(pbucket->pListNext!=NULL){245 pbucket->pListNext->pListPre=pbucket->pListPre;246 }247 if(pbucket->pPre!=NULL){248 pbucket->pPre->pNext=pbucket->pNext;249 }else{250 arBuckets[nIndex]=pbucket->pNext;251 }252 if(pbucket->pNext!=NULL){253 pbucket->pNext->pPre=pbucket->pPre;254 }255 --nNumOfElements;256 delete pbucket;257 return true;258 }else{259 pbucket=pbucket->pNext;260 }261 }262 return false;263 }264 }

HashTable.cpp

1 #pragma once 2 class Bucket 3 { 4 public: 5     Bucket(const char* arKey,void *value,unsigned long h); 6     ~Bucket(void); 7     unsigned long h; 8     unsigned int nKeyLength; 9     void *pData;10     const char *arKey;11     Bucket *pNext;12     Bucket *pPre;13     Bucket *pListNext;14     Bucket *pListPre;15 };16 #include "stdafx.h"17 #include "Bucket.h"18 19 20 Bucket::Bucket(const char* _arKey,void *value,unsigned long h):arKey(_arKey)21 {22     this->pData=value;23     this->h=h;24     this->pNext=NULL;25     this->pPre=NULL;26     this->pListNext=NULL;27     this->pListPre=NULL;28 }29 30 31 Bucket::~Bucket(void)32 {33 }

Bucket.cpp

1 // hashtables.cpp : 定义控制台应用程序的入口点。  2 //  3   4 #include "stdafx.h"  5 #include 
      
         6 #include "HashTable.h"  7 using namespace std;  8   9 int _tmain(int argc, _TCHAR* argv[]) 10 { 11     HashTable ht; 12     ht.add("name","max"); 13     ht.add("name","max"); 14     ht.add("name2","max2"); 15     ht.add("name3","max3"); 16     ht.add("name4","max4"); 17     ht.add("name5","max5"); 18     ht.add("name6","max6"); 19     ht.add("name7","max7"); 20     ht.add("name8","max8"); 21     ht.add("name9","max9"); 22     ht.add("name10","max10"); 23     ht.add("name11","max11"); 24     ht.add("name12","max12"); 25     ht.add("name13","max13"); 26     ht.add("name14","max14"); 27     ht.add("name15","max15"); 28     ht.add("name16","max16"); 29     ht.add("name17","max17"); 30     ht.add("name18","max18"); 31     ht.add("name19","max19"); 32     ht.add("name20","max20"); 33     ht.add("name21","max21"); 34     ht.add("name22","max22"); 35     ht.add("name23","max23"); 36     ht.add("name24","max24"); 37     ht.add("name25","max25"); 38     ht.add("name26","max26"); 39     ht.add("name27","max27"); 40     ht.add("name28","max28"); 41     ht.add("name29","max29"); 42     cout<<"------------------------------"<
       
        arKey<<";bucket value:"<<(char*)bucket->pData<<";"<
        
         pListNext; 48     } 49     cout<<"------------------------------"<
         
          arKey<<";bucket value:"<<(char*)bucket->pData<<";"<
          
           pListPre; 55     } 56      57     cout<<"------------------------------"<
           
            arKey<<";index:"<
            <
             
              pNext; 63 } 64 } 65 cout<<"------------------------------"<
              
               arKey<<";bucket value:"<<(char*)bucket->pData<<";"<
               
                pListNext; 87 } 88 cout<<"------------------------------"<
                
                 arKey<<";index:"<
                 <
                  
                   pNext; 94 } 95 } 96 cout<<"elemetes num "<
                   
                    <
                    
                     arKey<<";index:"<
                     <
                      
                       pNext;121 // }122 // }123 // cout<<"elemetes num "<
                       
                        <

main.cpp

转载于:https://www.cnblogs.com/HPhone/p/3534366.html

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