PAT 1009 Product of Polynomials (25 分)

#include <iostream>
using namespace std;
int main() {
    int n1, n2, a, cnt = 0;
    scanf("%d", &n1);
    double b, arr[1001] = {0.0}, ans[2001] = {0.0};
    for(int i = 0; i < n1; i++) {
        scanf("%d %lf", &a, &b);
        arr[a] = b;
    }
    scanf("%d", &n2);
    for(int i = 0; i < n2; i++) {
        scanf("%d %lf", &a, &b);
        for(int j = 0; j < 1001; j++)
            ans[j + a] += arr[j] * b;   //j+a次幂的系数 要加上b *arr中j次幂的系数值，这是a次幂的全部影响
    }
    for(int i = 2000; i >= 0; i--)
        if(ans[i] != 0.0) cnt++;
            printf("%d", cnt);
    for(int i = 2000; i >= 0; i--)
        if(ans[i] != 0.0)
            printf(" %d %.1f", i, ans[i]);
    return 0;
}