一天一点数据结构+算法：复习Hash Map

LinearMap就是普通的数组。

HashMap是自己做的哈希映射。

HashMap查找的时间复杂度为O(1)，十分快。二叉查找树的查找速度是O(LogN)，所以哈希在查找数据时表现很好。

但是，Hash并不适合做排序，而二叉查找树中和了查找和排序两个功能。

#include <vector>

template <class Key, class Value>
class HashMap //哈希映射

{
public:
    HashMap(int size = 101):arr(size){
    
     currentSize = 0;
    
    }

    void Put(const Key & k, const Value & v)
    {
        int pos = myhash(k);
        arr[pos] = DataEntry(k, v);
        ++currentSize;        
    }

    Value Get(const Key & k)
    {
        int pos = myhash(k);
        if(arr[pos].key == k)
            return arr[pos].value;
        else
            return Value();

    }

    unsigned hash(const Key & k) const
    {
    
        unsigned int hashVal = 0;
        const char *keyp = reinterpret_cast<const char *> (&k);
        for(size_t i = 0; i<sizeof(Key); i++)
            hashVal = 37 * hashVal + keyp[i];
        return hashVal;

    }

    int myhash(const Key & k) const
    {
    
      unsigned hashVal = hash(k);
      hashVal %= arr.size();
      return hashVal;
    }


private:

    struct DataEntry{
    
        Key key;
        Value value;

        DataEntry(const Key & k = Key(), const Value & v = Value()):
        key(k),value(v){}
    };

    std::vector<DataEntry> arr;

    int currentSize;
    
};

#include <vector>

template <class Key, class Value>
class LinearMap //线性运算

{
public:
    LinearMap(int size = 101):arr(size){
    
     currentSize = 0;
    
    }

    void Put(const Key & k, const Value & v)
    {
    
        arr[currentSize] = DataEntry(k,v);
        ++currentSize;
    
    }

    Value Get(const Key & k)
    {
    
        //线性查找
        for(size_t i = 0; i<currentSize; ++i) 
        {
        
            if(arr[i].key == k)
                return arr[i].value;
        }
    
        return Value();
    }

    
private:

    struct DataEntry{
    
        Key key;
        Value value;

        DataEntry(const Key & k = Key(), const Value & v = Value()):
        key(k),value(v){}
    };

    std::vector<DataEntry> arr;

    int currentSize;
    
};

#include <iostream>
#include <map>//二叉树映射，不是哈希映射
#include <hash_map>  //C++自己做的hash，头文件里不是
#include <string>
#include "LinearMap.h"
#include "HashMap.h"


using namespace std;

int main()
{
    cout << "红黑树映射" << endl;
    map<string,int> m;
    m["Bill"] = 98;
    m["Tom"] = 67;
    m["Marry"] = 100;

    cout << m["Tom"] << endl;

    //数组的优点
    int a[100000];
    for(int i = 0; i< 100000; i++)
        a[i] = i % 100;


    cout << a[8] << endl;

    LinearMap<string, int> lm;
    lm.Put("Bill", 99);
    lm.Put("Tom", 88);
    lm.Put("Marry", 77);
    cout << "LinearMap: " << lm.Get("Tom") << endl;
    
    //My HashMap
    cout << "MyHashMap: " << endl;
    HashMap<string, int> myHMap;

    cout << myHMap.hash("Bill") << endl;

    myHMap.Put("Bill", 999);
    myHMap.Put("Tom", 888);
    myHMap.Put("Marry",777);
    cout << myHMap.Get("Tom") << endl;

    cout << endl;

    cout << "微软做的哈希映射：" << endl;
    hash_map<string, int> hm;
    hm["Bill"] = 12;
    hm["Tom"] = 22;

    cout << hm["Tom"] << endl;


    return 0;
}