hdu 1154 Cutting a Polygon (Simple Geometry)
2013-05-28 22:15
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http://acm.hdu.edu.cn/showproblem.php?pid=1154
简单的计算几何题。因为没有看清题意,把直线看成线段了,所以WA了几次。
做法相当简单,我们只需要把直线于多边形的交点都求出来,然后每相邻两个交点取其中点,判断中点是否在多边形内。如果中点在多边形内,则当前线段在多边形内。这是一个很常见的判断方法。
代码(带模板)如下:
View Code
——written by Lyon
简单的计算几何题。因为没有看清题意,把直线看成线段了,所以WA了几次。
做法相当简单,我们只需要把直线于多边形的交点都求出来,然后每相邻两个交点取其中点,判断中点是否在多边形内。如果中点在多边形内,则当前线段在多边形内。这是一个很常见的判断方法。
代码(带模板)如下:
#include <cstdio> #include <cstring> #include <cmath> #include <set> #include <vector> #include <iostream> #include <algorithm> using namespace std; // Point class struct Point { double x, y; Point() {} Point(double x, double y) : x(x), y(y) {} } ; template<class T> T sqr(T x) { return x * x;} inline double ptDis(Point a, Point b) { return sqrt(sqr(a.x - b.x) + sqr(a.y - b.y));} // basic calculations typedef Point Vec; Vec operator + (Vec a, Vec b) { return Vec(a.x + b.x, a.y + b.y);} Vec operator - (Vec a, Vec b) { return Vec(a.x - b.x, a.y - b.y);} Vec operator * (Vec a, double p) { return Vec(a.x * p, a.y * p);} Vec operator / (Vec a, double p) { return Vec(a.x / p, a.y / p);} const double EPS = 1e-8; const double PI = acos(-1.0); inline int sgn(double x) { return fabs(x) < EPS ? 0 : (x < 0 ? -1 : 1);} bool operator < (Point a, Point b) { return a.x < b.x || (a.x == b.x && a.y < b.y);} bool operator == (Point a, Point b) { return sgn(a.x - b.x) == 0 && sgn(a.y - b.y) == 0;} inline double dotDet(Vec a, Vec b) { return a.x * b.x + a.y * b.y;} inline double crossDet(Vec a, Vec b) { return a.x * b.y - a.y * b.x;} inline double crossDet(Point o, Point a, Point b) { return crossDet(a - o, b - o);} inline double vecLen(Vec x) { return sqrt(dotDet(x, x));} inline double toRad(double deg) { return deg / 180.0 * PI;} inline double angle(Vec v) { return atan2(v.y, v.x);} inline double angle(Vec a, Vec b) { return acos(dotDet(a, b) / vecLen(a) / vecLen(b));} inline double triArea(Point a, Point b, Point c) { return fabs(crossDet(b - a, c - a));} inline Vec vecUnit(Vec x) { return x / vecLen(x);} inline Vec rotate(Vec x, double rad) { return Vec(x.x * cos(rad) - x.y * sin(rad), x.x * sin(rad) + x.y * cos(rad));} Vec normal(Vec x) { double len = vecLen(x); return Vec(- x.y / len, x.x / len); } // Line class struct Line { Point s, t; Line() {} Line(Point s, Point t) : s(s), t(t) {} Point point(double x) { return s + (t - s) * x; } Line move(double x) { // while x > 0 move to (s->t)'s left Vec nor = normal(t - s); nor = nor * x; return Line(s + nor, t + nor); } Vec vec() { return t - s;} } ; typedef Line Seg; inline bool onLine(Point x, Point a, Point b) { return sgn(crossDet(a - x, b - x)) == 0;} inline bool onLine(Point x, Line l) { return onLine(x, l.s, l.t);} inline bool onSeg(Point x, Point a, Point b) { return sgn(crossDet(a - x, b - x)) == 0 && sgn(dotDet(a - x, b - x)) < 0;} inline bool onSeg(Point x, Seg s) { return onSeg(x, s.s, s.t);} // 0 : not intersect // 1 : proper intersect // 2 : improper intersect int segIntersect(Point a, Point c, Point b, Point d) { Vec v1 = b - a, v2 = c - b, v3 = d - c, v4 = a - d; int a_bc = sgn(crossDet(v1, v2)); int b_cd = sgn(crossDet(v2, v3)); int c_da = sgn(crossDet(v3, v4)); int d_ab = sgn(crossDet(v4, v1)); if (a_bc * c_da > 0 && b_cd * d_ab > 0) return 1; if (onSeg(b, a, c) && c_da) return 2; if (onSeg(c, b, d) && d_ab) return 2; if (onSeg(d, c, a) && a_bc) return 2; if (onSeg(a, d, b) && b_cd) return 2; return 0; } inline int segIntersect(Seg a, Seg b) { return segIntersect(a.s, a.t, b.s, b.t);} // point of the intersection of 2 lines Point lineIntersect(Point P, Vec v, Point Q, Vec w) { Vec u = P - Q; double t = crossDet(w, u) / crossDet(v, w); return P + v * t; } inline Point lineIntersect(Line a, Line b) { return lineIntersect(a.s, a.t - a.s, b.s, b.t - b.s);} // Warning: This is a DIRECTED Distance!!! double pt2Line(Point x, Point a, Point b) { Vec v1 = b - a, v2 = x - a; return crossDet(v1, v2) / vecLen(v1); } inline double pt2Line(Point x, Line L) { return pt2Line(x, L.s, L.t);} double pt2Seg(Point x, Point a, Point b) { if (a == b) return vecLen(x - a); Vec v1 = b - a, v2 = x - a, v3 = x - b; if (sgn(dotDet(v1, v2)) < 0) return vecLen(v2); if (sgn(dotDet(v1, v3)) > 0) return vecLen(v3); return fabs(crossDet(v1, v2)) / vecLen(v1); } inline double pt2Seg(Point x, Seg s) { return pt2Seg(x, s.s, s.t);} Point ptOnLine(Point p, Point a, Point b) { Vec v = b - a; return a + v * (dotDet(v, p - a) / dotDet(v, v)); } inline Point ptOnLine(Point p, Line x) { return ptOnLine(p, x.s, x.t);} // Polygon class struct Poly { vector<Point> pt; Poly() { pt.clear();} ~Poly() {} Poly(vector<Point> pt) : pt(pt) {} Point operator [] (int x) const { return pt[x];} int size() { return pt.size();} double area() { double ret = 0.0; int sz = pt.size(); for (int i = 1; i < sz; i++) { ret += crossDet(pt[i], pt[i - 1]); } return fabs(ret / 2.0); } } ; // Circle class struct Circle { Point c; double r; Circle() {} Circle(Point c, double r) : c(c), r(r) {} Point point(double a) { return Point(c.x + cos(a) * r, c.y + sin(a) * r); } } ; inline bool ptOnCircle(Point x, Circle c) { return sgn(ptDis(c.c, x) - c.r) == 0;} // Cirlce operations int lineCircleIntersect(Line L, Circle C, double &t1, double &t2, vector<Point> &sol) { double a = L.s.x, b = L.t.x - C.c.x, c = L.s.y, d = L.t.y - C.c.y; double e = sqr(a) + sqr(c), f = 2 * (a * b + c * d), g = sqr(b) + sqr(d) - sqr(C.r); double delta = sqr(f) - 4.0 * e * g; if (sgn(delta) < 0) return 0; if (sgn(delta) == 0) { t1 = t2 = -f / (2.0 * e); sol.push_back(L.point(t1)); return 1; } t1 = (-f - sqrt(delta)) / (2.0 * e); sol.push_back(L.point(t1)); t2 = (-f + sqrt(delta)) / (2.0 * e); sol.push_back(L.point(t2)); return 2; } int lineCircleIntersect(Line L, Circle C, vector<Point> &sol) { Vec dir = L.t - L.s, nor = normal(dir); Point mid = lineIntersect(C.c, nor, L.s, dir); double len = sqr(C.r) - sqr(ptDis(C.c, mid)); if (sgn(len) < 0) return 0; if (sgn(len) == 0) { sol.push_back(mid); return 1; } Vec dis = vecUnit(dir); len = sqrt(len); sol.push_back(mid + dis * len); sol.push_back(mid - dis * len); return 2; } // -1 : coincide int circleCircleIntersect(Circle C1, Circle C2, vector<Point> &sol) { double d = vecLen(C1.c - C2.c); if (sgn(d) == 0) { if (sgn(C1.r - C2.r) == 0) { return -1; } return 0; } if (sgn(C1.r + C2.r - d) < 0) return 0; if (sgn(fabs(C1.r - C2.r) - d) > 0) return 0; double a = angle(C2.c - C1.c); double da = acos((sqr(C1.r) + sqr(d) - sqr(C2.r)) / (2.0 * C1.r * d)); Point p1 = C1.point(a - da), p2 = C1.point(a + da); sol.push_back(p1); if (p1 == p2) return 1; sol.push_back(p2); return 2; } void circleCircleIntersect(Circle C1, Circle C2, vector<double> &sol) { double d = vecLen(C1.c - C2.c); if (sgn(d) == 0) return ; if (sgn(C1.r + C2.r - d) < 0) return ; if (sgn(fabs(C1.r - C2.r) - d) > 0) return ; double a = angle(C2.c - C1.c); double da = acos((sqr(C1.r) + sqr(d) - sqr(C2.r)) / (2.0 * C1.r * d)); sol.push_back(a - da); sol.push_back(a + da); } int tangent(Point p, Circle C, vector<Vec> &sol) { Vec u = C.c - p; double dist = vecLen(u); if (dist < C.r) return 0; if (sgn(dist - C.r) == 0) { sol.push_back(rotate(u, PI / 2.0)); return 1; } double ang = asin(C.r / dist); sol.push_back(rotate(u, -ang)); sol.push_back(rotate(u, ang)); return 2; } // ptA : points of tangency on circle A // ptB : points of tangency on circle B int tangent(Circle A, Circle B, vector<Point> &ptA, vector<Point> &ptB) { if (A.r < B.r) { swap(A, B); swap(ptA, ptB); } double d2 = sqr(A.c.x - B.c.x) + sqr(A.c.y - B.c.y); double rdiff = A.r - B.r, rsum = A.r + B.r; if (d2 < sqr(rdiff)) return 0; double base = atan2(B.c.y - A.c.y, B.c.x - A.c.x); if (d2 == 0 && A.r == B.r) return -1; if (d2 == sqr(rdiff)) { ptA.push_back(A.point(base)); ptB.push_back(B.point(base)); return 1; } double ang = acos((A.r - B.r) / sqrt(d2)); ptA.push_back(A.point(base + ang)); ptB.push_back(B.point(base + ang)); ptA.push_back(A.point(base - ang)); ptB.push_back(B.point(base - ang)); if (d2 == sqr(rsum)) { ptA.push_back(A.point(base)); ptB.push_back(B.point(PI + base)); } else if (d2 > sqr(rsum)) { ang = acos((A.r + B.r) / sqrt(d2)); ptA.push_back(A.point(base + ang)); ptB.push_back(B.point(PI + base + ang)); ptA.push_back(A.point(base - ang)); ptB.push_back(B.point(PI + base - ang)); } return (int) ptA.size(); } // -1 : onside // 0 : outside // 1 : inside int ptInPoly(Point p, Poly &poly) { int wn = 0, sz = poly.size(); for (int i = 0; i < sz; i++) { if (onSeg(p, poly[i], poly[(i + 1) % sz])) return -1; int k = sgn(crossDet(poly[(i + 1) % sz] - poly[i], p - poly[i])); int d1 = sgn(poly[i].y - p.y); int d2 = sgn(poly[(i + 1) % sz].y - p.y); if (k > 0 && d1 <= 0 && d2 > 0) wn++; if (k < 0 && d2 <= 0 && d1 > 0) wn--; } if (wn != 0) return 1; return 0; } // if DO NOT need a high precision /* int ptInPoly(Point p, Poly &poly) { int sz = poly.size(); double ang = 0.0, tmp; for (int i = 0; i < sz; i++) { if (onSeg(p, poly[i], poly[(i + 1) % sz])) return -1; tmp = angle(poly[i] - p) - angle(poly[(i + 1) % sz] - p) + PI; ang += tmp - floor(tmp / (2.0 * PI)) * 2.0 * PI - PI; } if (sgn(ang - PI) == 0) return -1; if (sgn(ang) == 0) return 0; return 1; } */ // Convex Hull algorithms // return the number of points in convex hull // andwer's algorithm // if DO NOT want the points on the side of convex hull, change all "<" into "<=" int andrew(Point *pt, int n, Point *ch) { sort(pt, pt + n); int m = 0; for (int i = 0; i < n; i++) { while (m > 1 && crossDet(ch[m - 1] - ch[m - 2], pt[i] - ch[m - 2]) <= 0) m--; ch[m++] = pt[i]; } int k = m; for (int i = n - 2; i >= 0; i--) { while (m > k && crossDet(ch[m - 1] - ch[m - 2], pt[i] - ch[m - 2]) <= 0) m--; ch[m++] = pt[i]; } if (n > 1) m--; return m; } // graham's algorithm // if DO NOT want the points on the side of convex hull, change all "<=" into "<" Point origin; inline bool cmpAng(Point p1, Point p2) { return crossDet(origin, p1, p2) > 0;} inline bool cmpDis(Point p1, Point p2) { return ptDis(p1, origin) > ptDis(p2, origin);} void removePt(Point *pt, int &n) { int idx = 1; for (int i = 2; i < n; i++) { if (sgn(crossDet(origin, pt[i], pt[idx]))) pt[++idx] = pt[i]; else if (cmpDis(pt[i], pt[idx])) pt[idx] = pt[i]; } n = idx + 1; } int graham(Point *pt, int n, Point *ch) { int top = -1; for (int i = 1; i < n; i++) { if (pt[i].y < pt[0].y || (pt[i].y == pt[0].y && pt[i].x < pt[0].x)) swap(pt[i], pt[0]); } origin = pt[0]; sort(pt + 1, pt + n, cmpAng); removePt(pt, n); for (int i = 0; i < n; i++) { if (i >= 2) { while (!(crossDet(ch[top - 1], pt[i], ch[top]) <= 0)) top--; } ch[++top] = pt[i]; } return top + 1; } // Half Plane // The intersected area is always a convex polygon. // Directed Line class struct DLine { Point p; Vec v; double ang; DLine() {} DLine(Point p, Vec v) : p(p), v(v) { ang = atan2(v.y, v.x);} bool operator < (const DLine &L) const { return ang < L.ang;} DLine move(double x) { // while x > 0 move to v's left Vec nor = normal(v); nor = nor * x; return DLine(p + nor, v); } } ; Poly cutPoly(Poly &poly, Point a, Point b) { Poly ret = Poly(); int n = poly.size(); for (int i = 0; i < n; i++) { Point c = poly[i], d = poly[(i + 1) % n]; if (sgn(crossDet(b - a, c - a)) >= 0) ret.pt.push_back(c); if (sgn(crossDet(b - a, c - d)) != 0) { Point ip = lineIntersect(a, b - a, c, d - c); if (onSeg(ip, c, d)) ret.pt.push_back(ip); } } return ret; } inline Poly cutPoly(Poly &poly, DLine L) { return cutPoly(poly, L.p, L.p + L.v);} inline bool onLeft(DLine L, Point p) { return crossDet(L.v, p - L.p) > 0;} Point dLineIntersect(DLine a, DLine b) { Vec u = a.p - b.p; double t = crossDet(b.v, u) / crossDet(a.v, b.v); return a.p + a.v * t; } Poly halfPlane(DLine *L, int n) { Poly ret = Poly(); sort(L, L + n); int fi, la; Point *p = new Point ; DLine *q = new DLine ; q[fi = la = 0] = L[0]; for (int i = 1; i < n; i++) { while (fi < la && !onLeft(L[i], p[la - 1])) la--; while (fi < la && !onLeft(L[i], p[fi])) fi++; q[++la] = L[i]; if (fabs(crossDet(q[la].v, q[la - 1].v)) < EPS) { la--; if (onLeft(q[la], L[i].p)) q[la] = L[i]; } if (fi < la) p[la - 1] = dLineIntersect(q[la - 1], q[la]); } while (fi < la && !onLeft(q[fi], p[la - 1])) la--; if (la - fi <= 1) return ret; p[la] = dLineIntersect(q[la], q[fi]); for (int i = fi; i <= la; i++) ret.pt.push_back(p[i]); return ret; } // 3D Geometry void getCoor(double R, double lat, double lng, double &x, double &y, double &z) { lat = toRad(lat); lng = toRad(lng); x = R * cos(lat) * cos(lng); y = R * cos(lat) * sin(lng); z = R * sin(lat); } struct Point3 { double x, y, z; Point3() {} Point3(double x, double y, double z) : x(x), y(y), z(z) {} } ; typedef Point3 Vec3; Vec3 operator + (Vec3 a, Vec3 b) { return Vec3(a.x + b.x, a.y + b.y, a.z + b.z);} Vec3 operator - (Vec3 a, Vec3 b) { return Vec3(a.x - b.x, a.y - b.y, a.z - b.z);} Vec3 operator * (Vec3 a, double p) { return Vec3(a.x * p, a.y * p, a.z * p);} Vec3 operator / (Vec3 a, double p) { return Vec3(a.x / p, a.y / p, a.z / p);} bool operator < (Point3 a, Point3 b) { if (a.x != b.x) return a.x < b.x; if (a.y != b.y) return a.y < b.y; return a.z < b.z; } bool operator == (Point3 a, Point3 b) { return sgn(a.x - b.x) == 0 && sgn(a.y - b.y) == 0 && sgn(a.z - b.z) == 0;} inline double dotDet(Vec3 a, Vec3 b) { return a.x * b.x + a.y * b.y + a.z * b.z;} inline Vec3 crossDet(Vec3 a, Vec3 b) { return Vec3(a.y * b.z - a.z * b.y, a.z * b.x - a.x * b.z, a.x * b.y - a.y * b.x);} inline double vecLen(Vec3 x) { return sqrt(dotDet(x, x));} inline double angle(Vec3 a, Vec3 b) { return acos(dotDet(a, b) / vecLen(a) / vecLen(b));} inline double triArea(Point3 a, Point3 b, Point3 c) { return vecLen(crossDet(b - a, c - a));} struct Plane { Point3 p; Vec3 n; Plane() {} Plane(Point3 p, Vec3 n) : p(p), n(n) {} } ; // Warning: This is a DIRECTED Distance!!! inline double pt2Plane(Point3 p, Point3 p0, Vec3 n) { return dotDet(p - p0, n) / vecLen(n);} inline double pt2Plane(Point3 p, Plane P) { return pt2Plane(p, P.p, P.n);} // get projection on plane inline Point3 ptOnPlane(Point3 p, Point3 p0, Vec3 n) { return p + n * pt2Plane(p, p0, n);} inline Point3 ptOnPlane(Point3 p, Plane P) { return ptOnPlane(p, P.p, P.n);} inline bool ptInPlane(Point3 p, Point3 p0, Vec3 n) { return sgn(dotDet(p - p0, n)) == 0;} inline bool ptInPlane(Point3 p, Plane P) { return ptInPlane(p, P.p, P.n);} struct Line3 { Point3 s, t; Line3() {} Line3(Point3 s, Point3 t) : s(s), t(t) {} Vec3 vec() { return t - s;} } ; typedef Line3 Seg3; double pt2Line(Point3 p, Point3 a, Point3 b) { Vec3 v1 = b - a, v2 = p - a; return vecLen(crossDet(v1, v2)) / vecLen(v1); } inline double pt2Line(Point3 p, Line3 l) { return pt2Line(p, l.s, l.t);} double pt2Seg(Point3 p, Point3 a, Point3 b) { if (a == b) return vecLen(p - a); Vec3 v1 = b - a, v2 = p - a, v3 = p - b; if (sgn(dotDet(v1, v2)) < 0) return vecLen(v2); else if (sgn(dotDet(v1, v3)) > 0) return vecLen(v3); else return vecLen(crossDet(v1, v2)) / vecLen(v1); } inline double pt2Seg(Point3 p, Seg3 s) { return pt2Seg(p, s.s, s.t);} struct Tri { Point3 a, b, c; Tri() {} Tri(Point3 a, Point3 b, Point3 c) : a(a), b(b), c(c) {} } ; bool ptInTri(Point3 p, Point3 a, Point3 b, Point3 c) { double area1 = triArea(p, a, b); double area2 = triArea(p, b, c); double area3 = triArea(p, c, a); double area = triArea(a, b, c); return sgn(area1 = area2 + area3 - area) == 0; } inline bool ptInTri(Point3 p, Tri t) { return ptInTri(p, t.a, t.b, t.c);} // 0 : not intersect // 1 : intersect at only 1 point // 2 : line in plane int linePlaneIntersect(Point3 s, Point3 t, Point3 p0, Vec3 n, Point3 &x) { double res1 = dotDet(n, p0 - s); double res2 = dotDet(n, t - s); if (sgn(res2)) { if (ptInPlane(s, p0, n)) return 2; return 0; } x = s + (t - s) * (res1 / res2); // use general form : a * x + b * y + c * z + d = 0 // Vec3 v = s - t; // double k = (a * s.x + b * s.y + c * s.z + d) / (a * v.x + b * v.y + c * v.z); // x = s + (t - s) * k; return 1; } inline int linePlaneIntersect(Line3 l, Plane p, Point3 &x) { return linePlaneIntersect(l.s, l.t, p.p, p.n, x);} // ¡÷abc intersect with segment st bool triSegIntersect(Point3 a, Point3 b, Point3 c, Point3 s, Point3 t, Point3 &x) { Vec3 n = crossDet(b - a, c - a); if (sgn(dotDet(n, t - s)) == 0) return false; else { double k = dotDet(n, a - s) / dotDet(n, t - s); if (sgn(k) < 0 || sgn(k - 1) > 0) return false; x = s + (t - s) * k; return ptInTri(x, a, b, c); } } inline bool triSegIntersect(Tri t, Line3 l, Point3 &x) { return triSegIntersect(t.a, t.b, t.c, l.s, l.t, x);} // Warning: This is a DIRECTED Volume!!! inline double tetraVol(Point3 a, Point3 b, Point3 c, Point3 p) { return dotDet(p - a, crossDet(b - a, c - a)) / 6.0;} inline double tetraVol(Tri t, Point3 p) { return tetraVol(t.a, t.b, t.c, p);} /****************** template above *******************/ Poly poly; bool cmp(Point a, Point b) { if (sgn(a.x - b.x)) return a.x < b.x; return a.y < b.y; } double work(Seg seg) { int sz = poly.size(); vector<Point> ip; ip.clear(); seg = Seg(seg.s + (seg.s - seg.t) * 1e5, seg.t + (seg.t - seg.s) * 1e5); ip.push_back(seg.s); ip.push_back(seg.t); for (int i = 0; i < sz; i++) { if (segIntersect(Seg(poly[i], poly[(i + 1) % sz]), seg)) { ip.push_back(lineIntersect(Line(poly[i], poly[(i + 1) % sz]), seg)); } } sort(ip.begin(), ip.end(), cmp); sz = ip.size(); double sum = 0.0; for (int i = 1; i < sz; i++) { if (ptInPoly((ip[i - 1] + ip[i]) / 2.0, poly)) { sum += ptDis(ip[i - 1], ip[i]); } } return sum; } int main() { // freopen("in", "r", stdin); int n, m; while (cin >> n >> m && (n || m)) { poly.pt.clear(); double x, y; for (int i = 0; i < n; i++) { cin >> x >> y; poly.pt.push_back(Point(x, y)); } Seg tmp; for (int i = 0; i < m; i++) { cin >> tmp.s.x >> tmp.s.y >> tmp.t.x >> tmp.t.y; printf("%.3f\n", work(tmp)); } } return 0; }
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——written by Lyon
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