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模板模式--哈希表排序

#include <iostream>
#include <string>
#include <map>
#include <vector>
#include<algorithm>
using namespace std;
typedef pair<string,int>PAIR;
 bool cmp_by_value(const PAIR& p,const PAIR &a)
    {
        return p.second<a.second;
    }
struct cmp
{
    bool operator()(const string& k1, const string& k2) {
    return k1.length() <= k2.length();
  }
};


class Duck
{
    public:
    string name;
    int weight;
    Duck(const string &s,int w):name(s),weight(w){}
    bool operator<(const Duck &d)const
   {
       return weight<d.weight;
   }
};
void display(vector<PAIR>ducks)
{
    for(vector<PAIR>::iterator iter=ducks.begin();iter!=ducks.end();iter++)
    {
        cout<<(*iter).first<<"  "<<(*iter).second<<endl;
    }
}
int main()
{
    map<string,int,cmp>m;//相同时看perate中的比较有没有等号如果有则不会被替代
    m["Daffy"]=8;
    m["Dewey"]=2;
    m["Howard"]=7;
    m["Donald"]=10;
    vector<PAIR>ducks(m.begin(),m.end());
    cout<<"Before sorting"<<endl;
    display(ducks);
    cout<<"Afer sorting"<<endl;
    sort(ducks.begin(),ducks.end(),cmp_by_value);
    display(ducks);


    cout<<"下面是按key排序"<<endl;


    sort(ducks.begin(),ducks.end());
    display(ducks);




    return 0;
}