PAT 1009. Product of Polynomials (25)

题目地址： http://www.patest.cn/contests/pat-a-practise/1009

#include<iostream>

#include<iomanip>

#include<cstring>

#include<map>

#include<vector>



using namespace std;



const int MAXN  = 1000 + 10;

const double eps = 1e-9; 

struct Item {

        int e;

        double a;

        Item(int _e, double _a) {

                e = _e;

                a = _a;

        }

};

int main() {

        int k;

        while(cin >> k) {

                int e;

                double a;

                vector<Item> p;

                for (int i = 0; i < k; ++i) {

                        cin >> e >> a;

                        Item item(e, a);

                        p.push_back(item);

                }

                map<int, double> ans;

                cin >> k;

                for (int i = 0; i < k; ++i) {

                        cin >> e >> a;

                        for (int j = 0; j < p.size(); ++j) {

                                int ans_e = p[j].e + e;

                                double ans_a= p[j].a * a;

                                if (ans.count(ans_e)) {

                                        double x = ans[ans_e];

                                        if ((x + ans_a > -eps && x + ans_a < eps)) {

                                                ans.erase(ans_e);

                                        } else {

                                                ans[ans_e] += ans_a;

                                        }

                                } else {

                                        ans[ans_e] = ans_a;

                                }

                        }

                }

                cout << ans.size();

                for (map<int, double> :: reverse_iterator iter = ans.rbegin(); iter != ans.rend(); ++iter) {

                        cout << " " << iter->first << " ";

                        cout << fixed << setprecision(1)<< iter->second;

                }

                cout << endl;

        }

        return 0;

}