BZOJ 1038 [ZJOI 2008] 瞭望塔

学习半平面交，刚开始把边界的现在的1e6打了1e100于是爆炸...

//By Richard#include <cstdio>#include <algorithm>#include <cstring>#include <cstdlib>#include <cmath>#include <ctime>#define rep(x,y,z) for (int x=(y);(x)<=(z);(x)++)#define per(x,y,z) for (int x=(y);(x)>=(z);(x)--)#define log2(x) (31-__builtin_clz(x))#define mod (int)(1e9+7)#define inf 0x3f3f3f3f#define cls(x) memset(x,0,sizeof(x))#ifdef DEBUG#define debugdo(X) X#define debugndo(X)#define debugout(X) cout<<(#X)<<"="<<(X)<<endl#else#define debugdo(X)#define debugndo(X) X#define debugout(X)#endif // debug#ifdef ONLINE_JUDGE#define debugdo(X)#define debugndo(X)#define debugout(X)#endif#define putarray(x,n) rep(iiii,1,n) printf("%d ",x[iiii])#define mp make_pairusing namespace std;typedef pair<int,int> pairs;typedef long long LL;/////////////////////read4.0////////////////////////////////////template <typename T>inline void read(T &x){char ch;x=0;bool flag=false;ch=getchar();while (ch>'9'||ch<'0') {if (ch=='-') flag=true;ch=getchar();}while ((ch<='9'&&ch>='0')){x=x*10+ch-'0';ch=getchar();}if (flag) x*=-1;}template <typename T>inline void read(T &x,T &y){read(x);read(y);}template <typename T>inline void read(T &x,T &y,T &z){read(x);read(y);read(z);}/////////////////variables&functions////////////////////const int maxn=301;const double eps=0.000000000001;int n,cnt;#define angel anglestruct Point{    double x,y;    Point(int a,int b):x((double)a),y((double)b){}    Point(double a=0,double b=0):x(a),y(b){}    inline Point operator-(Point b)const{return Point(x-b.x,y-b.y);}    inline double operator*(Point b)const{return x*b.y-y*b.x;}}res[maxn],p[maxn];double mul(Point x,Point y,Point z){return (y.x-x.x)*(z.y-x.y)-(y.y-x.y)*(z.x-x.x);}struct Line{    Point x,y;    double angle;    Line(Point a=Point(0,0),Point b=Point(0,0),double e=0):x(a),y(b),angle(e){}    inline bool operator<(Line b)const{return abs(angle-b.angle)<eps?mul(x,b.x,b.y)>0:angel<b.angel;}    inline bool operator==(Line b)const{return abs(angel-b.angle)<eps;}}data[maxn];struct deque{    int top,bot,data[maxn];    ~deque(){top=1;bot=0;}    inline int front(){return data[bot];}    inline int front2(){return data[bot+1];}    inline int back(){return data[top-1];}    inline int back2(){return data[top-2];}    inline void pop_front(){bot++;}    inline void pop_back(){top--;}    inline bool empty(){return top<=bot;}    inline void push_front(int x){data[--bot]=x;}    inline void push_back(int x){data[top++]=x;}    inline bool judge(){return top>bot+1;}    inline bool judge2(){return top>bot+2;}}deq;Point intersect(Line a,Line b){    double k1,k2,t;    k1=(b.y-a.x)*(a.y-a.x);    k2=(a.y-a.x)*(b.x-a.x);    t=k1/(k1+k2);    return Point(b.y.x+(b.x.x-b.y.x)*t,b.y.y+(b.x.y-b.y.y)*t);}inline bool judge(Line x,Line y,Line z){    Point temp=intersect(x,y);    return (z.y-z.x)*(temp-z.x)<0;}void hpi(Line *a,int n)//Half-Plane Intersection{    sort(a+1,a+n+1);    int m=unique(a+1,a+n+1)-a-1;    deq.push_back(1);deq.push_back(2);    rep(i,3,m)    {        while (deq.judge()&&judge(a[deq.back2()],a[deq.back()],a[i])) deq.pop_back();        while (deq.judge()&&judge(a[deq.front2()],a[deq.front()],a[i])) deq.pop_front();        deq.push_back(i);    }    while (deq.judge2()&&judge(a[deq.back2()],a[deq.back()],a[deq.front()])) deq.pop_back();    while (deq.judge2()&&judge(a[deq.front2()],a[deq.front()],a[deq.back()])) deq.pop_front();    deq.push_back(deq.front());//  rep(i,deq.bot,deq.top-1) printf("%lf %lf %lf %lf\n",a[deq.data[i]].x.x,a[deq.data[i]].x.y,a[deq.data[i]].y.x,a[deq.data[i]].y.y);    rep(i,deq.bot,deq.top-2) res[++cnt]=intersect(a[deq.data[i]],a[deq.data[i+1]]);}int main(){    read(n);    rep(i,1,n) read(p[i].x);    rep(i,1,n) read(p[i].y);    p[0]=Point((double)p[1].x,1e6);    p[n+1]=Point((double)p[n].x,1e6);    double beforex=p[0].x,beforey=p[0].y;    //data[1]=Line(Point(),Point(beforex,beforey));    rep(i,1,n+1)     {//      if (y[i]>=beforey)                  data[i]=Line(Point(beforex,beforey),Point(p[i].x,p[i].y),atan2(p[i].y-beforey,p[i].x-beforex));//      else data[i-1]=Line(Point(x[i],y[i]),Point(beforex,beforey),atan2(beforey-y[i],beforex-x[i]));        beforex=p[i].x;beforey=p[i].y;    }    //data[n+1]=Line(Point(beforex,beforey),Point();    hpi(data,n+1);    double ans=1e18;    rep(i,1,cnt)    {        rep(j,1,n-1)         {            Point t(res[i].x,(double)(-1));            if (res[i].x>p[j].x&&res[i].x<=p[j+1].x) ans=min(ans,res[i].y-intersect(Line(p[j],p[j+1]),Line(t,res[i])).y);        }    }    rep(i,1,n)        rep(j,1,cnt-1)        {            Point t(p[i].x,(double)(-1));            if (p[i].x>res[j].x&&p[i].x<=res[j+1].x) ans=min(ans,intersect(Line(res[j],res[j+1]),Line(t,p[i])).y-p[i].y);        }    printf("%.3lf\n",ans);    return 0;}