1002. A+B for Polynomials

#include <iostream>
#include<map>
#include<iomanip>
#include<stdio.h>
using namespace std;

int main()
{
    map<int,double> polynomial;

    int n,input1;
    double input2;

        scanf("%d",&n);
        for (int i=0;i<n ;i++ ){
            cin>>input1>>input2;
          polynomial[input1]=input2;
        }

        scanf("%d",&n);
        for (int i=0;i<n ;i++ ){
        cin>>input1>>input2;
        if(polynomial.find(input1)==polynomial.end()){//represent try to find n in s,but not found situation.

          polynomial[input1]=input2;
        }
        else{
            polynomial[input1]=polynomial[input1]+input2;
        }
        if(polynomial[input1]==0)
            polynomial.erase(input1);
    }

    map<int,double>::reverse_iterator i;//can  use auto instead 
    cout<<polynomial.size();
    for (i=polynomial.rbegin();i!=polynomial.rend();i++){
        cout<<" "<<i->first<<" "<<fixed<<setprecision(1)<<i->second; ////fixed表示小数点右边有多少位数字
    }
    return 0;
}