1 条题解

  • 0
    @ 2025-5-6 19:02:18

    说明

    该程序用于判断一个多边形(钱币)能否通过另一个多边形(孔洞)。判断依据是钱币在自由下落过程中是否能完全穿过孔洞而不被卡住,即使轻微触碰边缘也视为合法。

    算法标签

    • 计算几何
    • 凸包算法
    • 多边形包含检测
    • 线段与多边形相交检测

    解题思路

    1. 问题分析:需要判断钱币多边形是否能通过孔洞多边形。关键在于钱币的最小宽度是否小于孔洞的最大内接线段长度。
    2. 输入处理:读取孔洞和钱币的多边形顶点坐标。
    3. 凸包计算:对钱币多边形计算凸包,以减少计算复杂度。
    4. 关键计算
      • 计算孔洞多边形的最大内接线段长度(max_polygon_inside_segment)。
      • 计算钱币多边形的最小宽度(Jinggai_problems)。
    5. 结果判断:如果钱币的最小宽度小于等于孔洞的最大内接线段长度,则合法;否则非法。

    分析

    • 凸包计算:使用ConvexHull函数计算钱币多边形的凸包,确保处理的是凸多边形。
    • 最大内接线段:通过遍历孔洞多边形的所有可能线段组合,找到最长的完全位于多边形内部的线段。
    • 最小宽度:通过旋转卡壳算法计算凸多边形的最小宽度。

    实现步骤

    1. 读取输入:处理多个测试用例,读取孔洞和钱币的多边形顶点。
    2. 计算孔洞特性:计算孔洞多边形的最大内接线段长度。
    3. 处理钱币:计算钱币多边形的凸包,然后计算其最小宽度。
    4. 结果输出:比较钱币的最小宽度和孔洞的最大内接线段长度,输出判断结果。

    代码解释

    • 数据结构
      • P类:表示二维点,包含基本的几何运算(如叉积、点积、距离计算等)。
      • Polygon:表示多边形,使用vector<P>存储顶点。
    • 关键函数
      • ConvexHull:计算给定点集的凸包。
      • max_polygon_inside_segment:计算多边形内最长的完全内接线段。
      • Jinggai_problems:计算凸多边形的最小宽度(旋转卡壳算法)。
    • 主逻辑
      • 读取测试用例数量T
      • 对于每个测试用例,读取孔洞和钱币的多边形顶点。
      • 计算孔洞的最大内接线段长度和钱币的最小宽度。
      • 输出判断结果(legalillegal)。

    该程序通过精确的几何计算和高效的算法,解决了多边形通过性问题,适用于类似的空间几何判断场景。

    代码

    #include<cstdio>
    #include<cstring>
    #include<cstdlib>
    #include<algorithm>
    #include<functional>
    #include<iostream>
    #include<cmath>
    #include<cctype>
    #include<ctime>
    #include<iomanip> 
    #include<vector>
    #include<string>
    #include<queue>
    #include<complex>
    #include<stack>
    #include<map>
    #include<sstream>
    using namespace std;
    #define For(i,n) for(int i=1;i<=n;i++)
    #define Fork(i,k,n) for(int i=k;i<=n;i++)
    #define Rep(i,n) for(int i=0;i<n;i++)
    #define ForD(i,n) for(int i=n;i;i--)
    #define ForkD(i,k,n) for(int i=n;i>=k;i--)
    #define RepD(i,n) for(int i=n;i>=0;i--)
    #define Forp(x) for(int p=Pre[x];p;p=Next[p])
    #define Forpiter(x) for(int &p=iter[x];p;p=Next[p])  
    #define Lson (o<<1)
    #define Rson ((o<<1)+1)
    #define MEM(a) memset(a,0,sizeof(a));
    #define MEMI(a) memset(a,127,sizeof(a));
    #define MEMi(a) memset(a,128,sizeof(a));
    #define INF (2139062143)
    #define F (100000007)
    #define pb push_back
    #define mp make_pair 
    #define fi first
    #define se second
    #define vi vector<int> 
    #define pi pair<int,int>
    #define SI(a) ((a).size())
    #define ALL(x) (x).begin(),(x).end()
    typedef long long ll;
    typedef long double ld;
    typedef unsigned long long ull;
    ll mul(ll a,ll b){return (a*b)%F;}
    ll add(ll a,ll b){return (a+b)%F;}
    ll sub(ll a,ll b){return (a-b+llabs(a-b)/F*F+F)%F;}
    void upd(ll &a,ll b){a=(a%F+b%F)%F;}
    int read()
    {
        int x=0,f=1; char ch=getchar();
        while(!isdigit(ch)) {if (ch=='-') f=-1; ch=getchar();}
        while(isdigit(ch)) { x=x*10+ch-'0'; ch=getchar();}
        return x*f;
    } 
    ll sqr(ll a){return a*a;}
    ld sqr(ld a){return a*a;}
    double sqr(double a){return a*a;}
    const double eps=1e-10;
    int dcmp(double x) {
        if (fabs(x)<eps) return 0; else return x<0 ? -1 : 1; 
    }
    ld PI = 3.141592653589793238462643383;
    class P{
    public:
        double x,y;
        P(double x=0,double y=0):x(x),y(y){}
        friend ld dis2(P A,P B){return sqr(A.x-B.x)+sqr(A.y-B.y);   }
        friend ld Dot(P A,P B) {return A.x*B.x+A.y*B.y; }
        friend ld Length(P A) {return sqrt(Dot(A,A)); }
        friend ld Angle(P A,P B) {
            if (dcmp(Dot(A,A))==0||dcmp(Dot(B,B))==0||dcmp(Dot(A-B,A-B))==0) return 0;
            return acos(max((ld)-1.0, min((ld)1.0, Dot(A,B) / Length(A) / Length(B) )) ); 
        }
    
        friend P operator- (P A,P B) { return P(A.x-B.x,A.y-B.y); }
        friend P operator+ (P A,P B) { return P(A.x+B.x,A.y+B.y); }
        friend P operator* (P A,double p) { return P(A.x*p,A.y*p); }
        friend P operator/ (P A,double p) { return P(A.x/p,A.y/p); }
        friend bool operator< (const P& a,const P& b) {return dcmp(a.x-b.x)<0 ||(dcmp(a.x-b.x)==0&& dcmp(a.y-b.y)<0 );}
    
    }; 
    P read_point() {
        P a;
        scanf("%lf%lf",&a.x,&a.y);
        return a;   
    } 
    bool operator==(const P& a,const P& b) {
        return dcmp(a.x-b.x)==0 && dcmp(a.y-b.y) == 0;
    } 
    typedef P V;
    
    double Cross(V A,V B) {return A.x*B.y - A.y*B.x;}
    double Area2(P A,P B,P C) {return Cross(B-A,C-A);}
    V Rotate(V A,double rad) {
        return V(A.x*cos(rad)-A.y*sin(rad),A.x*sin(rad)+A.y*cos(rad));
    } 
    // A 不是 0向量 
    V Normal(V A) { 
        double L = Length(A);
        return V(-A.y/L , A.x/L); 
    }
    
    namespace complex_G{
        typedef complex<double> Point;
        //real(p):实部 imag(p):虚部 conj(p):共轭 
        typedef Point Vector;
        double Dot(Vector A,Vector B) {return real(conj(A)*B); }
        double Cross(Vector A,Vector B) {return imag(conj(A)*B); }
        Vector Rotate(Vector A,double rad) {return A*exp(Point(0,rad)); }
    }
    //Cross(v,w)==0(平行)时,不能调这个函数 
    P GetLineIntersection(P p,V v,P Q,V w){
        V u = p-Q;
        double t = Cross(w,u)/Cross(v,w);
        return p+v*t;
    }
    P GetLineIntersectionB(P p,V v,P Q,V w){
        return GetLineIntersection(p,v-p,Q,w-Q);
    }
    
    double DistanceToLine(P p,P A,P B) {
        V v1 = B-A, v2 = p-A;
        return fabs(Cross(v1,v2))/Length(v1);
    }
    double DistanceToSegment(P p,P A,P B) {
        if (A==B) return Length(p-A);
        V v1 = B-A, v2 = p-A, v3 = p - B;
        if (dcmp(Dot(v1,v2))<0) return Length(v2);
        else if (dcmp(Dot(v1,v3))>0 ) return Length(v3);
        else return fabs(Cross(v1,v2) ) / Length(v1);
    }
    P GetLineProjection(P p,P A,P B) {
        V v=B-A;
        return A+v*(Dot(v,p-A)/Dot(v,v));
    }
    //规范相交-线段相交且交点不在端点 
    bool SegmentProperIntersection(P a1,P a2,P b1,P b2) { 
        double  c1 = Cross(a2-a1,b1-a1) , c2 = Cross(a2-a1,b2-a1),
                c3 = Cross(b2-b1,a1-b1) , c4 = Cross(b2-b1,a2-b1);
        return dcmp(c1)*dcmp(c2)<0 && dcmp(c3)*dcmp(c4)<0;
    }
    //点在线段上(不包含端点) 
    bool OnSegment(P p,P a1,P a2) {
        return dcmp(Cross(a1-p,a2-p)) == 0 && dcmp(Dot(a1-p,a2-p))<0;
    }
    double PolygonArea(P *p,int n) {
        double area=0;
        For(i,n-2) area+=Cross(p[i]-p[0],p[i+1]-p[0]);
        return area/2;
    }
    bool IsCollinear(P A,P B,P C,P D) {
        return !dcmp(Cross(A-B,C-D)) && !dcmp(Cross(A-B,C-B)) && !dcmp(DistanceToLine(A,C,D));
    } 
    /*欧拉公式: V+F-E=2 
    V-点数 F面数 E边数 */
    struct C{
        P c;
        double r,x,y;
        C(P c,double r):c(c),r(r),x(c.x),y(c.y){}
        P point(double a) {
            return P(c.x+cos(a)*r,c.y+sin(a)*r);
        }
    };
    
    struct Line{
        P p;
        V v;
        double ang;
        Line(){}
        Line(P p,V v):p(p),v(v) {ang=atan2(v.y,v.x); }
        bool operator<(const Line & L) const {
            return ang<L.ang;
        }
        P point(double a) {
            return p+v*a;
        }
    };
    int getLineCircleIntersection(Line L,C cir,double &t1,double &t2,vector<P> & sol) {
        if (dcmp(DistanceToLine(cir.c,L.p,L.p+L.v)-cir.r)==0) {
            P A=GetLineProjection(cir.c,L.p,L.p+L.v);
            sol.pb(A); 
            t1 = (A-L.p).x / L.v.x;  
            return 1;
        }
    
        double a = L.v.x, b = L.p.x - cir.c.x, c = L.v.y, d= L.p.y - cir.c.y;
        double e = a*a+c*c, f = 2*(a*b + c*d), g = b*b+d*d-cir.r*cir.r;
        double delta = f*f - 4*e*g;
        if (dcmp(delta)<0) return 0;
        else if (dcmp(delta)==0) {
            t1 = t2 = -f / (2*e); sol.pb(L.point(t1));
            return 1;
        } 
        t1 = (-f - sqrt(delta)) / (2*e); sol.pb(L.point(t1));
        t2 = (-f + sqrt(delta)) / (2*e); sol.pb(L.point(t2));
        return 2;
    }
    double angle(V v) {return atan2(v.y,v.x);}
    int getCircleCircleIntersection(C C1,C C2,vector<P>& sol) {
        double d = Length(C1.c-C2.c);
        if (dcmp(d)==0) {
            if (dcmp(C1.r - C2.r)==0) return -1; //2圆重合 
            return 0;
        }
        if (dcmp(C1.r+C2.r-d)<0) return 0;
        if (dcmp(fabs(C1.r-C2.r)-d)>0) return 0;
    
        double a = angle(C2.c-C1.c);
        double da = acos((C1.r*C1.r+d*d - C2.r*C2.r)/ (2*C1.r*d));
        P p1 = C1.point(a-da), p2 = C1.point(a+da);
        sol.pb(p1);
        if (p1==p2) return 1;
        sol.pb(p2);
        return 2; 
    }
    // Tangents-切线 
    int getTangents(P p,C c,V* v) {
        V u= c.c-p;
        double dist = Length(u);
        if (dist<c.r) return 0;
        else if (dcmp(dist-c.r)==0) {
            v[0]=Rotate(u,PI/2);
            return 1;
        } else {
            double ang = asin(c.r / dist);
            v[0]=Rotate(u,-ang);
            v[1]=Rotate(u,ang);
            return 2;
        }       
    }
    int getTangentsPoint(P p,C c,P *point) {
        V u= c.c-p;
        double dist = Length(u);
        if (dist<c.r) return 0;
        else if (dcmp(dist-c.r)==0) {
            point[0]=p;
            return 1;
        } else {
            V v[2];
            double ang = asin(c.r / dist);
            v[0]=Rotate(u,-ang);point[0]=GetLineProjection(c.c,p,p+v[0]);
            v[1]=Rotate(u,ang); point[1]=GetLineProjection(c.c,p,p+v[1]);
            return 2;
        }
    }
    //这个函数假设整数坐标和整数半径
    //double时要把int改成double 
    int getTangents(C A,C B,P* a,P* b) {
        int cnt=0;
        if (A.r<B.r) {swap(A,B),swap(a,b);}
        int d2 = (A.c.x-B.c.x)*(A.c.x-B.c.x) + (A.c.y-B.c.y)*(A.c.y-B.c.y);
        int rdiff = A.r-B.r;
        int rsum = A.r+B.r;
        if (d2<rdiff*rdiff) return 0;
        double base = atan2(B.y-A.y,B.x-A.x);
        if (d2==0 && A.r == B.r) return -1;
        if (d2 == rdiff*rdiff) {
            a[cnt] = A.point(base); b[cnt] = B.point(base); ++cnt;
            return 1;
        }
        double ang = acos((A.r-B.r)/sqrt(d2));
        a[cnt] = A.point(base+ang); b[cnt] = B.point(base+ang); ++cnt;
        a[cnt] = A.point(base-ang); b[cnt] = B.point(base-ang); ++cnt;
        if (d2==rsum*rsum) {
            a[cnt] = A.point(base); b[cnt] = B.point(PI+base); ++cnt;
        }
        else if (d2>rsum*rsum) {
            double ang = acos((A.r+B.r)/sqrt(d2));
            a[cnt] = A.point(base+ang); b[cnt] = B.point(PI+base+ang); ++cnt;
            a[cnt] = A.point(base-ang); b[cnt] = B.point(PI+base-ang); ++cnt;
        }
        return cnt; 
    }
    //Circumscribed-外接 
    C CircumscribedCircle(P p1,P p2,P p3) {
        double Bx = p2.x-p1.x, By= p2.y-p1.y;
        double Cx = p3.x-p1.x, Cy= p3.y-p1.y;
        double D = 2*(Bx*Cy-By*Cx);
        double cx = (Cy*(Bx*Bx+By*By)-By*(Cx*Cx+Cy*Cy))/D + p1.x;
        double cy = (Bx*(Cx*Cx+Cy*Cy)-Cx*(Bx*Bx+By*By))/D + p1.y;
        P p =P(cx,cy);
        return C(p,Length(p1-p));
    }
    //Inscribed-内接 
    C InscribedCircle(P p1,P p2,P p3) {
        double a = Length(p2-p3);
        double b = Length(p3-p1);
        double c = Length(p1-p2);
        P p = (p1*a+p2*b+p3*c)/(a+b+c);
        return C(p,DistanceToLine(p,p1,p2));
    }
    double torad(double deg) {
        return deg/180*acos(-1);
    }
    //把 角度+-pi 转换到 [0,pi) 上 
    double radToPositive(double rad) {
        if (dcmp(rad)<0) rad=ceil(-rad/PI)*PI+rad;
        if (dcmp(rad-PI)>=0) rad-=floor(rad/PI)*PI; 
        return rad;
    } 
    double todeg(double rad) {
        return rad*180/acos(-1);
    }
    
    //(R,lat,lng)->(x,y,z)
    void get_coord(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);
    }
    void print(double a) {
        printf("%.6lf",a); 
    }
    void print(P p) {
        printf("(%.6lf,%.6lf)",p.x,p.y);
    }
    template<class T>
    void print(vector<T> v) {
        sort(v.begin(),v.end());
        putchar('[');
        int n=v.size();
        Rep(i,n) {
            print(v[i]);
            if (i<n-1) putchar(','); 
        }
        puts("]");
    }
    // 把直线沿v平移
    // Translation-平移 
    Line LineTranslation(Line l,V v) {
        l.p=l.p+v;
        return l;
    }
    void CircleThroughAPointAndTangentToALineWithRadius(P p,Line l,double r,vector<P>& sol) {
        V e=Normal(l.v);
        Line l1=LineTranslation(l,e*r),l2=LineTranslation(l,e*(-r));
        double t1,t2;
        getLineCircleIntersection(l1,C(p,r),t1,t2,sol);
        getLineCircleIntersection(l2,C(p,r),t1,t2,sol);
    }
    void CircleTangentToTwoLinesWithRadius(Line l1,Line l2,double r,vector<P>& sol) {
        V e1=Normal(l1.v),e2=Normal(l2.v);
        Line L1[2]={LineTranslation(l1,e1*r),LineTranslation(l1,e1*(-r))},
             L2[2]={LineTranslation(l2,e2*r),LineTranslation(l2,e2*(-r))};
        Rep(i,2) Rep(j,2) sol.pb(GetLineIntersection(L1[i].p,L1[i].v,L2[j].p,L2[j].v));
    }
    void CircleTangentToTwoDisjointCirclesWithRadius(C c1,C c2,double r,vector<P>& sol) {
        c1.r+=r; c2.r+=r;
        getCircleCircleIntersection(c1,c2,sol);
    }
    //确定4个点能否组成凸多边形,并按顺序(不一定是逆时针)返回 
    bool ConvexPolygon(P &A,P &B,P &C,P &D) {
        if (SegmentProperIntersection(A,C,B,D)) return 1;
        swap(B,C);
        if (SegmentProperIntersection(A,C,B,D)) return 1;
        swap(D,C);
        if (SegmentProperIntersection(A,C,B,D)) return 1;
        return 0;
    }
    bool IsParallel(P A,P B,P C,P D) {
        return dcmp(Cross(B-A,D-C))==0;
    }
    bool IsPerpendicular(V A,V B) {
        return dcmp(Dot(A,B))==0;
    }
    //先调用ConvexPolygon 求凸包并确认是否是四边形
    // Trapezium-梯形 Rhombus-菱形  
    bool IsTrapezium(P A,P B,P C,P D){
        return IsParallel(A,B,C,D)^IsParallel(B,C,A,D);
    }
    bool IsParallelogram(P A,P B,P C,P D) {
        return IsParallel(A,B,C,D)&&IsParallel(B,C,A,D);
    }
    bool IsRhombus(P A,P B,P C,P D) {
        return IsParallelogram(A,B,C,D)&&dcmp(Length(B-A)-Length(C-B))==0;
    }
    bool IsRectangle(P A,P B,P C,P D) {
        return IsParallelogram(A,B,C,D)&&IsPerpendicular(B-A,D-A);
    }
    bool IsSquare(P A,P B,P C,P D) {
        return IsParallelogram(A,B,C,D)&&IsPerpendicular(B-A,D-A)&&dcmp(Length(B-A)-Length(C-B))==0;
    }
    
    //chord-弦 arc-弧 
    double ArcDis(double chord,double r) {
        return 2*asin(chord/2/r)*r;
    } 
    typedef vector<P> Polygon ;
    int isPointInPolygon(P p,Polygon poly) {
        int wn=0;
        int n=poly.size();
        Rep(i,n) {
            if (OnSegment(p,poly[i],poly[(i+1)%n])) return -1; //edge
            int k=dcmp(Cross(poly[(i+1)%n]-poly[i],p-poly[i]));
            int d1 = dcmp(poly[i].y-p.y);
            int d2 = dcmp(poly[(i+1)%n].y-p.y);
            if ( k > 0 && d1 <= 0 && d2 > 0 ) wn++;
            if ( k < 0 && d2 <= 0 && d1 > 0 ) wn--;
        }
        if (wn!=0) return 1; //inside
        return 0; //outside
    }
    
    int ConvexHull(P *p,int n,P *ch) {
        sort(p,p+n);
        int m=0;
        Rep(i,n) {
            while(m>1 && Cross(ch[m-1]-ch[m-2],p[i]-ch[m-2])<=0) m--;
            ch[m++]=p[i];
        }
        int k=m;
        RepD(i,n-2) {
            while(m>k && Cross(ch[m-1]-ch[m-2],p[i]-ch[m-2])<=0) m--;
            ch[m++]=p[i];
        }
        if ( n > 1 ) m--;
        return m;
    }
    //把两点式转为一般式 ax+by+c=0 
    void Two_pointFormToGeneralForm(P A,P B,double &a,double &b,double &c){
        a = A.y - B.y;
        b = B.x - A.x;
        c = Cross(A,B);
    }
    //有向直线A->B 切割多边行poly 可能返回单点线段 O(n)
    Polygon CutPolygon(Polygon poly,P A,P B){
        Polygon newpoly;
        int n=poly.size();
        Rep(i,n) {
            P C = poly[i];
            P D = poly[(i+1)%n];
            if (dcmp(Cross(B-A,C-A))>=0)  newpoly.pb(C);
            if (dcmp(Cross(B-A,C-D))) {
                P ip = GetLineIntersection(A,B-A,C,D-C);
                if (OnSegment(ip,C,D)) newpoly.pb(ip);
            }
        }
        return newpoly;
    }
    double PolygonArea(Polygon &p) {
        double area=0;
        int n=p.size();
        For(i,n-2) area+=Cross(p[i]-p[0],p[i+1]-p[0]);
        return area/2;
    } 
    
    //线上不算 
    bool OnLeft(Line L,P p) {
        return Cross(L.v,p-L.p)>0;
    } 
    P GetIntersection(Line a,Line b) {
        V u=a.p-b.p;
        double t = Cross(b.v,u) / Cross(a.v, b.v);
        return a.p + a.v*t;
    }
    int HalfplaneIntersection(Line *L, int n, P* poly) {
        sort(L,L+n);
        int fi,la;
        P *p = new P[n];
        Line *q = new Line[n];
        q[fi=la=0 ] = L[0];
        For(i,n-1) {
            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(Cross(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] = GetIntersection(q[la-1],q[la]);
        }
        while(fi < la && !OnLeft(q[fi],p[la-1])) la--;
        if (la-fi<=1) return 0; 
        p[la] = GetIntersection(q[la],q[fi]);
    
        int m=0;
        Fork(i,fi,la) poly[m++]=p[i];
        return m;
    } 
    
    // hypot(double x,double y); return sqrt(x*x+y*y)
    
    double Jinggai_problems(P *p,int n) {
        int q=1;
        double ans=INF;
        Rep(i,n) {
            while(fabs(Area2(p[i],p[(i+1)%n],p[(q+1)%n]))> fabs(Area2(p[i],p[(i+1)%n],p[q] )) ) 
                q=(q+1)%n;
            ans = min( ans, (double)DistanceToSegment(p[q],p[i],p[(i+1)%n]) );          
        }
        return ans;
    }
    // rotating for rect
    double rec_rotating_calipers(P *p,int n) {
        int q=1;
        double ans1=1e15,ans2=1e15;
        int l=0,r=0;
        Rep(i,n) {
            while(dcmp(fabs(Area2(p[i],p[(i+1)%n],p[(q+1)%n])) - fabs(Area2(p[i],p[(i+1)%n],p[q] ))) >0  ) 
                q=(q+1)%n;
            while (dcmp(Dot(p[(i+1)%n]-p[i],p[(r+1)%n]-p[r]))>0 )  r=(r+1)%n;
            if (!i) l=q;
            while (dcmp(Dot(p[(i+1)%n]-p[i],p[(l+1)%n]-p[l]))<0 )  l=(l+1)%n;
            double d = Length(p[(i+1)%n]-p[i]);
            double h = fabs(Area2(p[i],p[(i+1)%n],p[q] ))/d;
            double w=(Dot(p[(i+1)%n]-p[i],p[r]-p[i]) - Dot(p[(i+1)%n]-p[i],p[l]-p[i]) ) /d;
            ans1=min(ans1,2*(h+w)),ans2=min(ans2,h*w);
        }
        printf("%.2lf %.2lf\n",ans2,ans1);
    }
    
    
    //去共线化 
    void simplify(Polygon& poly) {
        Polygon ans;
        int n=SI(poly);
        Rep(i,n) {
            if (dcmp(Cross(poly[i]-poly[(i+1)%n],poly[(i+1)%n]-poly[(i+2)%n]))!=0)
                ans.pb(poly[(i+1)%n]);
        }
        n=SI(ans);
        cout<<n<<endl;
        Rep(i,n) printf("%.4lf %.4lf\n",ans[i].x,ans[i].y);
    }
    
    int getSegCircleIntersection(Line L,C cir,vector<P> & sol) {
        if (dcmp(DistanceToLine(cir.c,L.p,L.p+L.v)-cir.r)==0) {
            P A= GetLineProjection(cir.c,L.p,L.p+L.v);
            if (OnSegment(A,L.p,L.p+L.v) || L.p==A || L.p+L.v==A  ) 
                sol.pb(A);
            return sol.size();
        }
        double t1,t2;
        double a = L.v.x, b = L.p.x - cir.c.x, c = L.v.y, d= L.p.y - cir.c.y;
        double e = a*a+c*c, f = 2*(a*b + c*d), g = b*b+d*d-cir.r*cir.r;
        double delta = f*f - 4*e*g;
        if (dcmp(delta)<0) return 0;
        else if (dcmp(delta)==0) {
            t1 = -f / (2*e); 
            if (dcmp(t1)>=0&&dcmp(t1-1)<=0) {
                sol.pb(L.point(t1));
            }
            return sol.size();
        } 
        t1 = (-f - sqrt(delta)) / (2*e); if (dcmp(t1)>=0&&dcmp(t1-1)<=0) sol.pb(L.point(t1));
        t2 = (-f + sqrt(delta)) / (2*e); if (dcmp(t2)>=0&&dcmp(t2-1)<=0) sol.pb(L.point(t2));
        if(SI(sol)==2 && t1>t2) swap(sol[1],sol[0]);
        return sol.size();
    }
    int isPointInOrOnCircle(P p,C c) {
        return dcmp(Length(p-c.c)-c.r)<=0;
    }
    
    // Triangle(O,A,B) and Circle(O,m)
    double CircleTriangleArea(P A,P B,double m) {
        double ans=0;
        C c=C(P(),m); P O=c.c;
        if (A==O||B==O) return 0;
        bool b = isPointInOrOnCircle(A,c);
        bool b2 = isPointInOrOnCircle(B,c);
        double opr;
        if (dcmp(Area2(O,A,B))>=0) opr=1; else opr=-1;
        if (b&&b2) {
            ans+=opr*fabs(Area2(A,B,O))/2; 
        } else if (!b&&!b2){
            Line l=Line(A,B-A);
            vector<P> sol;
            getSegCircleIntersection(l,c,sol);
            if (SI(sol)==2) {
                ans+=opr*fabs(Area2(sol[0],sol[1],O))/2;
                ans+=opr*m*m/2*(Angle(A,sol[0])+Angle(sol[1],B));
            } else {
                ans+=opr*m*m/2*(Angle(A,B));
            }
        } else {
            Line l=Line(A,B-A);
            vector<P> sol;
            getSegCircleIntersection(l,c,sol);
            if (SI(sol)==2) {
                ans+=opr*fabs(Area2(sol[0],sol[1],O))/2;
                ans+=opr*m*m/2*(Angle(A,sol[0])+Angle(sol[1],B));
            } else if(b) { 
                ans+=opr*fabs(Area2(sol[0],A,O))/2;
                ans+=opr*m*m/2*(Angle(sol[0],B));
            } else {
                ans+=opr*fabs(Area2(sol[0],B,O))/2;
                ans+=opr*m*m/2*(Angle(sol[0],A));
            }
        }
        return ans;
    }
    double max_polygon_inside_segment(Polygon p) {
        int n=SI(p);
        double ans=0;
        Rep(i,n) Fork(j,i+1,n-1) {
            P A=p[i],B=p[j];
            if (A==B) continue;
            Polygon poly;
            poly.pb(A); poly.pb(B);
            Rep(k,n) {
                P C=p[k],D=p[(k+1)%n];
                if (IsParallel(A,B,C,D)) {
                    if (IsCollinear(A,B,C,D)) {
                        poly.pb(C);
                        poly.pb(D);
                    }
                } else {
                    P t=GetLineIntersectionB(A,B,C,D);
                    poly.pb(t);
                }
            }
            sort(ALL(poly));
            poly.erase(unique(ALL(poly)),poly.end());
            int sz=SI(poly);
            double l=0; bool fl=0;
            For(i,sz-1) {
                P m=(poly[i]+poly[i-1])/2;
                if (isPointInPolygon(m,p)) {
                    if(!fl) l=Length(poly[i]-poly[i-1]);
                    else l+=Length(poly[i]-poly[i-1]);
                    ans=max(ans,l);
                    fl=1;
                }else fl=0;
            }
    
        }
        return ans;
    }
    P a[100],ch[100];
    Polygon b;
    int main()
    {
    //  freopen("D.in","r",stdin);
    //  freopen(".out","w",stdout);
        int T=read();
        while(T--) {
            int k=read();
            b.resize(k);
            Rep(i,k) b[i]=read_point();
            double len2=max_polygon_inside_segment(b);
            int n=read();
            Rep(i,n) a[i]=read_point();
            int m=ConvexHull(a,n,ch);
            double len=Jinggai_problems(ch,m);
            puts(len<=len2 ? "legal" : "illegal");
    
        } 
        return 0;
    }
    • 1

    信息

    ID
    2830
    时间
    1000ms
    内存
    256MiB
    难度
    10
    标签
    递交数
    2
    已通过
    1
    上传者