PAT 甲级 1002 A+B for Polynomials

题目链接：https://pintia.cn/problem-sets/994805342720868352/problems/994805526272000000

题意

给出两个多项式，输出二者相加后非零项的总个数及其次方、系数。

代码

#include <bits/stdc++.h>
using namespace std;
int main() {
    map<int, double> poly;
    for (int i = 0; i < 2; i++) {
        int n; cin >> n;
        for (int j = 0; j < n; j++) {
            int x; double y; cin >> x >> y;
            poly[x] += y;
        }
    }
    vector<pair<int, double>> res;
    for (auto it = poly.rbegin(); it != poly.rend(); ++it) {
        if (it->second != 0.0) {
            res.emplace_back(it->first, it->second);
        }
    }
    cout << res.size();
    for (auto pr : res) {
        cout << ' ' << pr.first << ' ' << setiosflags(ios::fixed) << setprecision(1) << pr.second;
    }
}