1002 A+B for Polynomials (25 分)

#include<iostream>
#include<algorithm>
#include<string>
#include<string.h>
#include<map>
#include<stack>
#include<queue>
#include <unordered_map>
using namespace std;
#define MAX 3000005
#define  ll long long
map<int,double>a;
int main()
{
    //ios::sync_with_stdio(false);
    int t=1;
    //cin>>t;
    while(t--)
    {
        int n,m;
        cin>>n;
        int q,ji=0;
        double u;
        while(n--)
        {
            cin>>q>>u;
            a[q]+=u;
        }
        cin>>m;
        while(m--)
        {
            cin>>q>>u;
            a[q]+=u;
        }
        map<int,double>::iterator it=a.begin();
        while(it!=a.end())
        {
            if(it->second)ji++;
            it++;
        }

        cout<<ji;
        it=a.end();
        it--;
        while(1)
        {
            if(it->second)
            {
                cout<<" "<<it->first;
                printf(" %.1lf",it->second);
            }
            if(it==a.begin())break;
            it--;

        }
        cout<<endl;



    }
}