關鍵詞：map鍵值對

 1 #include<iostream>
 2
 
 #include<map>
 3 #include<cmath>//要包含
 4 using namespace std;
 5 int main(){
 6     //freopen("in2.txt","r",stdin);
 7     int n;
 8     cin >> n;
 9     map<int,int> m;
10     for(int i = 0;i<n;i++){
11         int buf;
12         cin >> buf;
13         m[abs(buf)]++;
14
 
     }
15     int total = 0;
16     for(map<int,int>::iterator it = m.begin();it!=m.end();it++){
17         if(it->second > 1){
18             total++;
19         }
20     }
21     cout << total;
22     return 0;
23 }

CCF 201403-1 相反數