FOJ 2110 Star

Overpower often go to the playground with classmates. They play and chat on the playground. One day, there are a lot of stars in the sky. Suddenly, one of Overpower’s classmates ask him: “How many acute triangles whose inner angles are less than 90 degrees (regarding stars as points) can be found? Assuming all the stars are in the same plane”. Please help him to solve this problem.

The first line of the input contains an integer T (T≤10), indicating the number of test cases.

For each test case:

The first line contains one integer n (1≤n≤100), the number of stars.

The next n lines each contains two integers x and y (0≤|x|, |y|≤1,000,000) indicate the points, all the points are distinct.

For each test case, output an integer indicating the total number of different acute triangles.

130 010 05 1000

1 

给你一些点叫你求你能构成锐角三角形的个数，a, b, c三条边，a^2+b^2<c^2&&a^2+c^2<b^2&&c^2+b^2<a^2即可

AC代码：

# include <stdio.h>
typedef long long int ll;
struct node {ll x, y;
};
node s[110];
ll func(node a, node b){return (a.x-b.x)*(a.x-b.x)+(a.y-b.y)*(a.y-b.y);
}
int main(){int t, n, i, j, k;ll a, b, c;scanf("%d", &t);while(t--){scanf("%d", &n);for(i=1; i<=n; i++){scanf("%I64d%I64d", &s[i].x, &s[i].y);}if(n<=2){printf("0\n");continue;}int ans=0;for(i=1; i<=n-2; i++){for(j=i+1; j<=n-1; j++){for(k=j+1; k<=n; k++){a=func(s[i], s[j]);b=func(s[i], s[k]);c=func(s[j], s[k]);if(a+b>c&&a+c>b&&b+c>a){ans++;}}}}printf("%d\n", ans);}return 0;
}