思路:对于每个人 都会有n-1个半片面 加上x>0,y>0,1-x-y>0(这里的1抽象为总长)
代码是粘贴的 原来写的不见了 orz............
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// LA2218 Triathlon // Rujia Liu #include <cstdio> #include <cmath> #include <vector> #include <algorithm> using namespace std; struct Point { double x, y; Point(double x=0, double y=0):x(x),y(y) { } }; typedef Point Vector; Vector operator + (const Vector& A, const Vector& B) { return Vector(A.x+B.x, A.y+B.y); } Vector operator - (const Point& A, const Point& B) { return Vector(A.x-B.x, A.y-B.y); } Vector operator * (const Vector& A, double p) { return Vector(A.x*p, A.y*p); } double Dot(const Vector& A, const Vector& B) { return A.x*B.x + A.y*B.y; } double Cross(const Vector& A, const Vector& B) { return A.x*B.y - A.y*B.x; } double Length(const Vector& A) { return sqrt(Dot(A, A)); } Vector Normal(const Vector& A) { double L = Length(A); return Vector(-A.y/L, A.x/L); } double PolygonArea(vector<Point> p) { int n = p.size(); double area = 0; for(int i = 1; i < n-1; i++) area += Cross(p[i]-p[0], p[i+1]-p[0]); return area/2; } // 有向直线。它的左边就是对应的半平面 struct Line { Point P; // 直线上任意一点 Vector v; // 方向向量 double ang; // 极角,即从x正半轴旋转到向量v所需要的角(弧度) Line() {} Line(Point P, Vector v):P(P),v(v){ ang = atan2(v.y, v.x); } bool operator < (const Line& L) const { return ang < L.ang; } }; // 点p在有向直线L的左边(线上不算) bool OnLeft(const Line& L, const Point& p) { return Cross(L.v, p-L.P) > 0; } // 二直线交点,假定交点惟一存在 Point GetLineIntersection(const Line& a, const Line& b) { Vector u = a.P-b.P; double t = Cross(b.v, u) / Cross(a.v, b.v); return a.P+a.v*t; } const double INF = 1e8; const double eps = 1e-6; // 半平面交主过程 vector<Point> HalfplaneIntersection(vector<Line> L) { int n = L.size(); sort(L.begin(), L.end()); // 按极角排序 int first, last; // 双端队列的第一个元素和最后一个元素的下标 vector<Point> p(n); // p[i]为q[i]和q[i+1]的交点 vector<Line> q(n); // 双端队列 vector<Point> ans; // 结果 q[first=last=0] = L[0]; // 双端队列初始化为只有一个半平面L[0] for(int i = 1; i < n; i++) { while(first < last && !OnLeft(L[i], p[last-1])) last--; while(first < last && !OnLeft(L[i], p[first])) first++; q[++last] = L[i]; if(fabs(Cross(q[last].v, q[last-1].v)) < eps) { // 两向量平行且同向,取内侧的一个 last--; if(OnLeft(q[last], L[i].P)) q[last] = L[i]; } if(first < last) p[last-1] = GetLineIntersection(q[last-1], q[last]); } while(first < last && !OnLeft(q[first], p[last-1])) last--; // 删除无用平面 if(last - first <= 1) return ans; // 空集 p[last] = GetLineIntersection(q[last], q[first]); // 计算首尾两个半平面的交点 // 从deque复制到输出中 for(int i = first; i <= last; i++) ans.push_back(p[i]); return ans; } const int maxn = 100 + 10; int V[maxn], U[maxn], W[maxn]; int main() { int n; while(scanf("%d", &n) == 1 && n) { for(int i = 0; i < n; i++) scanf("%d%d%d", &V[i], &U[i], &W[i]); for(int i = 0; i < n; i++) { int ok = 1; double k = 10000; vector<Line> L; for(int j = 0; j < n; j++) if(i != j) { if(V[i] <= V[j] && U[i] <= U[j] && W[i] <= W[j]) { ok = 0; break; } if(V[i] >= V[j] && U[i] >= U[j] && W[i] >= W[j]) continue; // x/V[i]+y/U[i]+(1-x-y)/W[i] < x/V[j]+y/U[j]+(1-x-y)/W[j] // ax+by+c>0 double a = (k/V[j]-k/W[j]) - (k/V[i]-k/W[i]); double b = (k/U[j]-k/W[j]) - (k/U[i]-k/W[i]); double c = k/W[j] - k/W[i]; Point P; Vector v(b, -a); if(fabs(a) > fabs(b)) P = Point(-c/a, 0); else P = Point(0, -c/b); L.push_back(Line(P, v)); } if(ok) { // x>0, y>0, x+y<1 ==> -x-y+1>0 L.push_back(Line(Point(0, 0), Vector(0, -1))); L.push_back(Line(Point(0, 0), Vector(1, 0))); L.push_back(Line(Point(0, 1), Vector(-1, 1))); vector<Point> poly = HalfplaneIntersection(L); if(poly.empty()) ok = 0; } if(ok) printf("Yes "); else printf("No "); } } return 0; }