hashmap的C++實現

按照hashmap的基本原理用C++實現了簡單的基本功能，復雜的實現參考C++庫的源碼，C++最新的標準庫里已經有以下四種基于hashtable的容器：

unordered_set?(C++11)?unordered_multiset?(C++11)?unordered_map?(C++11)?unordered_multimap?(C++11)。具體參考：http://en.cppreference.com/w/

/** HashMap.h* Author: luxiaoxun*/#ifndef HASHMAP_H_ #define HASHMAP_H_#include <iostream> using namespace std;//List all the integer number no less than 57 total number is 28 //And each number is about half of its next number static int prime[28] = {57, 97, 193, 389, 769,1543, 3079, 6151, 12289, 24593,49157, 98317, 196613, 393241, 786433,1572869, 3145739, 6291469, 12582917, 25165843,50331653, 100663319, 201326611, 402653189, 805306457,1610612741 };class HashMapUtil { public:static int find_NextPrimeNumber(int current){//Find the next prime number by searching in the prime number listint i = 0;for( ; i < 28 ; i++ )if(current < prime[i])break;return prime[i]; //return the next larger prime. } };template <class Key, class Value, class HashFunc, class EqualKey> class HashMap { private:template <class _Key, class _Value>class KeyNode{public:_Value value; //Store the value_Key key; //Store the keywordint used;//if the type of Value/Key is your own class, make sure they can handle copy constructor and operator =KeyNode():used(0){}KeyNode(const KeyNode & kn){value = kn.value;key = kn.key;used = kn.used;}KeyNode & operator=(const KeyNode & kn){if(this == &kn) return *this;value = kn.value;key = kn.key;used = kn.used;return *this;}};public:HashMap();~HashMap();bool insert(const Key& hashKey, const Value& value);bool remove(const Key& hashKey);void rehash(); //use it when rehashingValue& find(const Key& hashKey);const Value& operator [](const Key& hashKey) const;Value& operator [](const Key& hashKey);private:HashFunc hash;EqualKey equal;HashMapUtil hml;KeyNode<Key ,Value> *table;int size; //current number of itmesint capacity; //capacity of the arraystatic const double loadingFactor;int findKey(const Key& hashKey); //find the index of a key };template<class Key , class Value , class HashFunc , class EqualKey> const double HashMap<Key, Value, HashFunc, EqualKey>::loadingFactor = 0.9;template<class Key , class Value , class HashFunc , class EqualKey> HashMap<Key, Value, HashFunc, EqualKey>::HashMap() {hash = HashFunc();equal = EqualKey();hml = HashMapUtil();capacity = hml.find_NextPrimeNumber(0); //initialize the capacity with first primer 57//resize the table with capacity because an extra one is used//to return the NULL type of Value in the function findtable = new KeyNode<Key,Value>[capacity+1];for(int i = 0 ; i < capacity ; i++) //initialize the tabletable[i].used = 0;size = 0; }template<class Key, class Value, class HashFunc, class EqualKey> HashMap<Key, Value, HashFunc, EqualKey>::~HashMap() {delete []table; }template<class Key, class Value, class HashFunc, class EqualKey> bool HashMap<Key, Value, HashFunc, EqualKey>::insert(const Key& hashKey, const Value& value) {int index = hash(hashKey)%capacity;//cout<<"Index is "<<index<<endl;if(table[index].used == 1) //the key-value's hash is unique {//cout<<"The key-value must be unique!"<<endl;return false;}table[index].used = 1; //modify the KeyNodetable[index].key = hashKey;table[index].value = value;size++;//if the table's size is too large ,then rehash itif (size >= capacity * loadingFactor)rehash();return true; }template<class Key, class Value, class HashFunc, class EqualKey> void HashMap<Key, Value, HashFunc, EqualKey>::rehash() {int pastsize = capacity;//create a new array to copy the information in the old tablecapacity = hml.find_NextPrimeNumber(capacity);KeyNode<Key,Value>* tmp = new KeyNode<Key,Value>[capacity];for(int i = 0 ; i < pastsize ; i++){if(table[i].used == 1) //copy the KeyNode into the tmp array {tmp[i] = table[i];}}delete []table; //release the memory of the old table table = new KeyNode<Key,Value>[capacity+1]; //resize the tablefor(int i = 0 ; i < capacity ; i++) //initialize the table {table[i].used = 0;}for(int i = 0 ; i < pastsize ; i++) //insert the item into the table one by one {if(tmp[i].used == 1)insert(tmp[i].key, tmp[i].value);}delete []tmp; //delete the tmp array }template<class Key, class Value, class HashFunc, class EqualKey> bool HashMap<Key, Value, HashFunc, EqualKey>::remove(const Key& hashKey) {int index = findKey(hashKey); //find the index of the keyif(index < 0) //if find modify the flag with 0,else print out "no such key!" {cout<<"No such Key!"<<endl;return false;}else{table[index].used = 0;size--;return true;} }template<class Key, class Value, class HashFunc, class EqualKey> Value& HashMap<Key, Value, HashFunc, EqualKey>::find(const Key& hashKey) {int index = findKey(hashKey);if(index < 0) //if index <0 ,not found,else return the index {cout<<"can not find the key!"<<endl;return table[capacity].value; //return NULL }else{return table[index].value;} }template<class Key, class Value, class HashFunc, class EqualKey> const Value& HashMap<Key, Value, HashFunc, EqualKey>::operator[](const Key& hashKey) const {return find(hashKey); //overload the operation to return the value of the element }template<class Key, class Value, class HashFunc, class EqualKey> Value& HashMap<Key, Value, HashFunc, EqualKey>::operator[](const Key& hashKey) {return find(hashKey); //overload the operation to return the value of the element }template<class Key, class Value, class HashFunc, class EqualKey> int HashMap<Key, Value, HashFunc, EqualKey>::findKey(const Key& hashKey) {int index = hash(hashKey)%capacity;if ((table[index].used != 1) || !equal(table[index].key,hashKey))return -1;elsereturn index; }#endif /* HASHMAP_H_ */

這里實現的key必須是unique的，否則就要處理沖突的問題，可以通過[]操作修改對應的value，但是不能通過[]添加value，標準庫里的是可以的。

C++編譯器不支持模板頭文件和實現代碼分離的編譯，如果的類實現和類聲明分別放在cpp文件和h頭文件里，那么在測試代碼里include要加上實現的代碼，比如加上#include"HashMap.cpp"。使用hashmap，需要自己提供針對key的hash函數對象和equal函數對象，測試代碼：

#include "HashMap.h" #include <string> #include <iostream> using namespace std;//Hash function you provided must be correspond to the type of the Key class HashFunc { public:int operator()(const string & key ){int hash = 0;for(int i = 0; i < key.length(); ++i){hash = hash << 7 ^ key[i];}return (hash & 0x7FFFFFFF);} };//Equal function you provided to check whether two Keys are equal //must be correspond to the type of the Key class EqualKey { public:bool operator()(const string & A ,const string & B){if(A.compare(B) == 0)return true; //if equal return trueelsereturn false; //else false } };int main() {HashMap<string,string,HashFunc,EqualKey> hm;hm.insert("hello" , "you");hm.insert("why" , "dream");hm.insert("java" ,"good");hm.insert("welcome" ,"haha");hm.insert("welcome" ,"hehe"); //error, key-value must be unique cout<<"after insert:"<<endl;cout<<hm.find("welcome")<<endl;cout<<hm.find("java")<<endl;cout<<hm["why"]<<endl;cout<<hm["hello"]<<endl;if(hm.remove("hello"))cout<<"remove is ok"<<endl; //remove is okcout<<hm.find("hello")<<endl; //not exist print NULL hm["why"] = "love"; //modify the value cout<<hm["why"]<<endl;return 0; } ? ? 本文轉自阿凡盧博客園博客，原文鏈接：http://www.cnblogs.com/luxiaoxun/archive/2012/09/02/2667782.html，如需轉載請自行聯系原作者
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