(PAT)1009. Product of Polynomials (25)

#include<iostream>
#include<string>
#include<vector>
#include<map>
#include<utility>
#include<algorithm>
#include<iomanip>
using namespace std;

class Pol
{

public :
	map<int,double>  coe;
	Pol operator*(const Pol& pol_b)
	{
		Pol pol_c;
		map<int,double>::const_iterator it_a=coe.begin();
		while(it_a!=coe.end())
		{
			map<int,double>::const_iterator it_b=pol_b.coe.begin();
			while(it_b!=pol_b.coe.end())
			{
				(pol_c.coe)[it_a->first+it_b->first]+=it_a->second*it_b->second;
				it_b++;
			}
			it_a++;

		}
		return pol_c;
	}
	void add(int key,double value)
	{
		coe[key]+=value;
	}

};
ostream& operator<<(ostream& os,const Pol& pol)
{
	cout.setf(ios::fixed);
	cout.precision(1);
	int sum=0;
	map<int,double>::const_reverse_iterator rev_it=pol.coe.rbegin();
	while(rev_it!=pol.coe.rend())
	{
		if(rev_it->second!=0)sum++;
		rev_it++;
	}
	cout<<sum;
	rev_it=pol.coe.rbegin();
	while(rev_it!=pol.coe.rend())
	{
		if(rev_it->second!=0)
		{
			cout<<" "<<rev_it->first<<" "<<rev_it->second;
		}
		rev_it++;
	}
	return cout;
}
int main()
{
	int len_a;
	int len_b;
	Pol pol_a;
	Pol pol_b;
	cin>>len_a;
	for(int i=0;i<len_a;i++)
	{
		int key;
		double val;
		cin>>key>>val;
		pol_a.add(key,val);
	}
	cin>>len_b;
	for(int i=0;i<len_b;i++)
	{
		int key;
		double val;
		cin>>key>>val;
		pol_b.add(key,val);
	}
	Pol pol_c=pol_a*pol_b;
	cout<<pol_c;
	
}

ps:這題主要回顧一下C++風格寫法以及map的應用。