题解:看这篇博文：http://blog.csdn.net/tri_integral/article/details/9772243
#include<cstdio> #include<cstring> #include<iostream> #include<algorithm> #include<vector> #include<string> #include<map> #include<set> #include<cmath> #include<sstream> #include<queue> #include<utility> #define MAXN 360050 #define eps 1e-8 #define PI acos(-1.0) #define INF 0x3f3f3f3f #define REP(i,n) for(int i=0; i<n; i++) #define FOR(i,s,t) for(int i=s; i<=t; i++) #define show(x) { cerr<<">>>"<<#x<<" = "<<x<<endl; } #define showtwo(x,y) { cerr<<">>>"<<#x<<"="<<x<<" "<<#y<<" = "<<y<<endl; } using namespace std; int n,r; double x[MAXN]; int dcmp(double x) { if(fabs(x) < eps) return 0; else return x < 0 ? -1 : 1; } int main() { //freopen("E:\acm\input.txt","r",stdin); int test_count = 1; while(cin>>n>>r) { if(n==0 && r==0) break; REP(i,n) cin>>x[i]; sort(x,x+n); x[n] = 360; long long ans = (long long)n*(n-1)*(n-2)/6; REP(i,n) { long long dis; if(dcmp(x[i]-180) < 0) dis = upper_bound(x,x+n,x[i]+180+eps)- x - i - 1; else dis = n - i + upper_bound(x,x+n,x[i]-180+eps) - x - 1; ans -= dis*(dis-1)/2; } printf("Case %d: ",test_count++); cout<<ans<<endl; } }