hashtable的C++实现

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hashtable的C++实现，使用两种常用的解决冲突的方式，使用时需要自己提供针对HashedObj的hash函数。

1、分离连接法（separate chaining）

#include <vector>#include <list>using namespace std;template <typename HashedObj>class HashTable{  public:    explicit HashTable(int size = 101);    void makeEmpty()    {        for(int i = 0; i < theLists.size(); i++)            theLists[i].clear();    }    bool contains(const HashedObj & x) const    {        const list<HashedObj> & whichList = theLists[myhash(x)];        return find(whichList.begin(), whichList.end(), x) != whichList.end();    }    bool remove(const HashedObj & x)    {        list<HashedObj> & whichList = theLists[myhash(x)];        typename list<HashedObj>::iterator itr = find(whichList.begin(), whichList.end(), x);        if(itr == whichList.end())            return false;        whichList.erase(itr);        --currentSize;        return true;    }    bool insert(const HashedObj & x)    {        list<HashedObj> & whichList = theLists[myhash(x)];        if(find(whichList.begin(), whichList.end(), x) != whichList.end())            return false;        whichList.push_back(x);        if(++currentSize > theLists.size())            rehash();        return true;    }  private:    vector<list<HashedObj> > theLists;   // The array of Lists    int  currentSize;    void rehash()    {        vector<list<HashedObj> > oldLists = theLists;        // Create new double-sized, empty table        theLists.resize(2 * theLists.size());        for(int j = 0; j < theLists.size(); j++)            theLists[j].clear();        // Copy table over        currentSize = 0;        for(int i = 0; i < oldLists.size(); i++)        {            typename list<HashedObj>::iterator itr = oldLists[i].begin();            while(itr != oldLists[i].end())                insert(*itr++);        }    }    int myhash(const HashedObj & x) const    {        int hashVal = hash(x);        hashVal %= theLists.size();        if(hashVal < 0)            hashVal += theLists.size();        return hashVal;    }};

2、使用探测法（probing hash tables）

template <typename HashedObj>class HashTable{  public:    explicit HashTable(int size = 101) : array(size)    {        makeEmpty();    }    void makeEmpty()    {        currentSize = 0;        for(int i = 0; i < array.size(); i++)            array[i].info = EMPTY;    }    bool contains(const HashedObj & x) const    {        return isActive(findPos(x));    }    bool insert(const HashedObj & x)    {        // Insert x as active        int currentPos = findPos(x);        if(isActive(currentPos))            return false;        array[currentPos] = HashEntry(x, ACTIVE);        if(++currentSize > array.size()/2)            rehash();        return true;    }    bool remove(const HashedObj & x)    {        int currentPos = findPos(x);        if(!isActive(currentPos))            return false;        array[currentPos].info = DELETED;        return true;    }    enum EntryType { ACTIVE, EMPTY, DELETED };  private:    struct HashEntry    {         HashedObj element;         EntryType info;         HashEntry(const HashedObj & e = HashedObj(), EntryType i = EMPTY )           : element(e), info(i) { }    };    vector<HashEntry> array;    int currentSize;    int findPos(const HashedObj & x) const    {        int offset = 1;        int currentPos = myhash(x);        while(array[currentPos].info != EMPTY && array[currentPos].element != x)        {            currentPos += offset;  // Compute ith probe            offset += 2;            if(currentPos >= array.size())                currentPos -= array.size();        }        return currentPos;    }    bool isActive(int currentPos) const    {        return array[currentPos].info == ACTIVE;    }    void rehash()    {        vector<HashEntry> oldArray = array;        // Create new double-sized, empty table        array.resize(2*oldArray.size());        for(int j = 0; j < array.size(); j++)            array[j].info = EMPTY;        // Copy table over        currentSize = 0;        for(int i = 0; i < oldArray.size(); i++)            if(oldArray[i].info == ACTIVE)                insert(oldArray[i].element);    }    int myhash(const HashedObj & x) const;};

作者：阿凡卢

出处：http://www.cnblogs.com/luxiaoxun/

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