题目链接:点击这里
#include<iostream>
#include<algorithm>
#include<string>
#include<cstdio>
#include<cstring>
#include<cmath>
#include<stack>
#include<queue>
#include<map>
#include<set>
using namespace std;
typedef long long ll;
const int MOD = 10000007;
const int INF = 0x3f3f3f3f;
const double PI = acos(-1.0);
const int maxn = 510;
struct point {
int x, y;
}a[maxn];
int get(int i, int j)
{
return (a[i].x-a[j].x)*(a[i].x-a[j].x) + (a[i].y-a[j].y)*(a[i].y-a[j].y);
}
int main()
{
int n;
scanf("%d", &n);
for(int i = 1; i <= n; ++i)
scanf("%d%d", &a[i].x, &a[i].y);
int cnt = 0;
for(int i = 1; i <= n; ++i)
{
for(int j = i + 1; j <= n; ++j)
{
for(int k = j + 1; k <= n; ++k)
{
int ij = get(i,j);
int ik = get(i,k);
int jk = get(j,k);
double dij = sqrt(1.0*ij);
double dik = sqrt(1.0*ik);
double djk = sqrt(1.0*jk);
if(dij+dik>djk && dij+djk>dik && dik+djk>dij) //三角形
{
if(ij>ik+jk || ik>ij+jk || jk>ij+ik) //钝角
cnt++;
}
}
}
}
printf("%d\n", cnt);
return 0;
}