PAT1009

不难，只要注意0项不输出，从大到小输出即可。
 1 #include<iostream>
 2 #include<map>
 3 #include<utility>
 4 #include<iterator>
 5 #include<iomanip>
 6 using namespace std;
 7 
 8 int main()
 9 {
10     int ain, bin;
11     while(cin>>ain)
12     {
13         map<int, double>  a, b, c;
14         for(int i=0; i < ain; ++i)
15         {
16             int key; double value;
17             cin>>key>>value;
18             a[key] = value;
19         }
20         cin>>bin;
21         for(int i=0; i < bin; ++i)
22         {
23             int key; double value;
24             cin>>key>>value;
25             b[key] = value;
26         }
27         map<int,double>::iterator a_iter = a.begin();
28         for(; a_iter != a.end(); ++a_iter)
29         {
30             map<int,double>::iterator b_iter = b.begin();
31             for(; b_iter != b.end(); ++b_iter)
32             {
33                 int k = a_iter->first + b_iter->first;
34                 c[k] += a_iter->second*b_iter->second;
35             }
36         }
37         map<int, double>::reverse_iterator c_riter = c.rbegin();
38         int num=0;
39         for(; c_riter != c.rend(); ++c_riter)
40             if(c_riter->second != 0)
41                 ++num;
42         cout<<num;
43         for(c_riter = c.rbegin(); c_riter != c.rend(); ++c_riter)
44             if(c_riter->second != 0)
45                 cout<<fixed<<setprecision(1)<<" "<<c_riter->first<<" "<<c_riter->second;
46         cout<<endl;
47     }
48     return 0;
49 }