题目

1009 Product of Polynomials （25 分)
This time, you are supposed to find A×B where A and B are two polynomials.

Input Specification:
Each input file contains one test case. Each case occupies 2 lines, and each line contains the information of a polynomial:

K N
​1
​​ a
​N
​1
​​
​​ N
​2
​​ a
​N
​2
​​
​​ ... N
​K
​​ a
​N
​K
​​
​​

where K is the number of nonzero terms in the polynomial, N
​i
​​ and a
​N
​i
​​
​​ (i=1,2,⋯,K) are the exponents and coefficients, respectively. It is given that 1≤K≤10, 0≤N
​K
​​ <⋯<N
​2
​​ <N
​1
​​ ≤1000.

Output Specification:
For each test case you should output the product of A and B in one line, with the same format as the input. Notice that there must be NO extra space at the end of each line. Please be accurate up to 1 decimal place.

Sample Input:
2 1 2.4 0 3.2
2 2 1.5 1 0.5
Sample Output:
3 3 3.6 2 6.0 1 1.6

分析

这道题是一个多项式的乘法，利用map进行遍历即可，也可以使用数组的方法，注意系数为0的情况要被删除！
从这道题里面可以巩固一下map的遍历及自定义排序输出！

代码

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

int main(){
    map<int,float> m1;
    map<int,float,greater<int>> m3;
    
    int n;
    cin>>n;
    for(int i=0;i<n;i++){
        int x;float y;
        cin>>x>>y;
        m1[x]=y;
    }
    
    cin>>n;
    for(int i=0;i<n;i++){
        map<int,float>::iterator it1=m1.begin();
        int x;float y;
        cin>>x>>y;
        for(;it1!=m1.end();it1++){
            int u = it1->first+x;
            float v = it1->second*y;
            if(m3.find(u)==m3.end()){
                m3[u]=v;
            }else{
                m3[u]+=v;
                if(m3[u]==0.0){
                    m3.erase(u);
                }
            }
        }
    }
    cout<<m3.size();
    map<int,float,greater<int>>::iterator it3=m3.begin();
    for(;it3!=m3.end();it3++){
            printf(" %d %.1f",it3->first,it3->second);
    }
}