CCF真题
#include<iostream> #include<vector> #include<string> #include<algorithm> #include<stack> #include<queue> #include<map> #include<set> #include<climits> #include<cstdbool> #include<cmath> using namespace std; int main() { int n; cin>>n; set<int>s; vector<int>arr(n); int res=0; for(int i=0;i<n;i++) { cin>>arr[i]; if(s.count(-arr[i])){ res++; }else{ s.insert(arr[i]); } } cout<<res; return 0; }
