PAT甲级真题 1002 A+B for Polynomials (25分) C++实现

题目

This time, you are supposed to find A+B where A and B are two polynomials.
Input
Each input file contains one test case. Each case occupies 2 lines, and each line contains the information of a polynomial: K N1 aN1 N2 aN2 … NK aNK, where K is the number of nonzero terms in the polynomial, Ni and aNi (i=1, 2, …, K) are the exponents and coefficients, respectively. It is given that 1 <= K <= 10，0 <= NK < … < N2 < N1 <=1000.
Output
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
Sample Output
3 2 1.5 1 2.9 0 3.2

大意：求多项式加法，精确到小数点后1位。

思路

用map存储指数和系数的映射关系，如果出现系数为0，则从map中删去。

map是自动排序的，只需后序遍历输出即可。

注意题目要求精确到小数点后1位，加上控制输出即可。

代码

#include 
#include 
#include 
using namespace std;

int main(){
    map<int, float> coefMap;
    for (int i=0; i<2; i++){
        int k;
        cin >> k;
        for (int j=0; j<k; j++){
            int exp;
            float coef;
            cin >> exp >> coef;
            coefMap[exp] += coef;
            if (coefMap[exp]==0){
                coefMap.erase(exp);
            }
        }
    }
    cout << coefMap.size();
    for (auto it=coefMap.rbegin(); it!=coefMap.rend(); ++it){
        cout << " " << it->first << " "  << fixed << setprecision(1) << it->second;
    }
    cout << endl;
    return 0;
}