1009 Product of Polynomials (25 point(s))

1009 Product of Polynomials (25 point(s))

This time, you are supposed to find A×B where A and B are two polynomials.

Example:

#include<iostream>
#include<cstdio>
#include<cmath>
#include<vector>
#include<map>

using namespace std;

struct Item {
    int    exp;
    double co;
};

void input(vector<Item> &N)
{
    Item item;
    int K;
    cin >> K;
    for(int i = 0; i < K; i++) {
        cin >> item.exp >> item.co;
        N.push_back(item);
    }
}

int main()
{
    int K1, K2;
    vector<Item> N1;
    vector<Item> N2;
    map<int, double> N3;
    input(N1);
    input(N2);
    for(auto &x : N1) {
        for(auto &y : N2) {
            int exp = x.exp + y.exp;
            N3[exp] += x.co * y.co;
        }
    }
    int count = 0;
    for(auto &x : N3)
        if(fabs(x.second) >= 0.1)
            count++;
    cout << count;
    for(auto x = N3.rbegin(); x != N3.rend(); x++)
        if(fabs(x->second) >= 0.1)
            printf(" %d %.1f", x->first, x->second);
    cout << endl;
}

思路：

利用 stl/map 是红黑树实现的原理，保存并更新对应 exp 的系数，最后统计系数绝对值 >=0.1 的项数，输出