问题

1002 A+B for 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 sum 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 to 1 decimal place.

Sample Input:
2 1 2.4 0 3.2
2 2 1.5 1 0.5
结尾无空行
Sample Output:
3 2 1.5 1 2.9 0 3.2
结尾无空行

思路

利用map<int,double,greater>按key可以从大到小自动排序的特性来存储多项式相加后的结果。第一遍先让第一个多项式放进map中，第二遍对于第二个多项式，如果key已存在，则让系数相加即可，如果key不存在，新增一对key value。最后利用迭代器输出map即可。

代码

#include <bits/stdc++.h>
using namespace std;

map<int,double,greater<int>> mp;

int n,m;

int main(){
    int iNum;
    double fNum;
    cin>>n;
    for (int i = 0; i < n; ++i) {
        getchar();
        scanf("%d %lf",&iNum,&fNum);
        mp[iNum] = fNum;
    }
    cin>>m;
    for (int j = 0; j < m; ++j) {
        getchar();
        scanf("%d %lf",&iNum,&fNum);
        if(mp.count(iNum)!=0){
            mp[iNum] = mp[iNum] + fNum;
            if(mp[iNum] == 0){
                mp.erase(iNum);
            }
        }
        else
            mp[iNum] = fNum;
    }
    map<int,double>::iterator it;
    --it;
    cout<<mp.size();
    if(mp.size()!=0)
        cout<<" ";
    int count = 0;
    for (it = mp.begin();it!=mp.end();++it) {
        ++count;
        printf("%d %.1f",it->first,it->second);
        if(count != mp.size())
            cout<<" ";
    }
    cout<<endl;
    return 0;
}

总结

几个坑要注意：
1.系数的结果要保留一位小数。
2.两个系数相加可能等于0，这时要删除key。
3.对于结果多项式，如果为0，只需要输出一个0即可，后面不能接空格，注意边界情况的输出格式，否则会一直卡在23分。

标签：map,int,多项式,相加,mp,key,iNum,fNum
来源： https://blog.csdn.net/qq_19272233/article/details/119300580