题目链接：fzu 2110 Star
题目大意：给出若干的点，计算出用这些点可以组成的锐角三角形的个数。
解题思路:枚举三个点，然后按照向量相乘大于0作为锐角来考虑。
#include#include typedef long long ll; const int N = 105; struct point { ll x, y; void get() { scanf("%lld%lld", &x, &y); } }p[N]; int n; void init() { scanf("%d", &n); for (int i = 0; i < n; i++) p[i].get(); } bool isOK(point a, point b, point c) { point pi, qi; pi.x = b.x - a.x, pi.y = b.y - a.y; qi.x = c.x - a.x, qi.y = c.y - a.y; if (pi.x * qi.x + pi.y * qi.y > 0) return true; return false; } bool judge(point a, point b, point c) { if (isOK(a, b, c) && isOK(b, a, c) && isOK(c, a, b) ) return true; return false; } int solve() { int ans = 0; for (int i = 0; i < n; i++) for (int j = i + 1; j < n; j++) for (int k = j + 1; k < n; k++) if (judge(p[i], p[j], p[k])) ans++; return ans; } int main() { int cas; scanf("%d", &cas); while (cas--) { init(); printf("%d\n", solve()); } return 0; }