Bzoj 4445 [SCOI2015] xiao Convex want to run

Main topic: A convex hull, a random point makes it with the first two points of the area than the other two adjacent points small area of the probability

According to the test Instructions column equation, the ratio of the intersection area of N lines to the area of the original convex hull is finally obtained.

1#include <bits/stdc++.h>2 #defineMAXN 1000103 #defineEPS 1e-104 using namespacestd;5 Doubleans,s1,s2;6 structp{7     Doublex, y;8PDoubleA=0,Doubleb=0) {x=a,y=b;}9 };Ten structl{ One P A, b; A     Doubleang; - }; - intSgnDoublex) { the     return(x>eps)-(x<-EPS); - } -Poperator-(P a,p b) { -     returnP (a.x-b.x,a.y-b.y); + } - Double operator*(P a,p b) { +     returna.x*b.y-a.y*b.x; A } at BOOL operator<(L a,l b) { -     if(SGN (a.ang-b.ang)! =0)returna.ang<B.ang; -     return(A.A-B.A) *a.b<0; - } - intN; - P S[MAXN]; in L L[MAXN],Q[MAXN]; P P[MAXN]; - inth,r,tot,cnt; to L get_line (P a,p b,p c,p D) { + l l; -     Doublea=-a.y-d.y+b.y+c.y; the     Doubleb=-b.x-c.x+a.x+d.x; *     Doublec=-a.x*b.y-d.x*c.y+b.x*a.y+c.x*D.y; $L.b=p (b,-a);Panax Notoginseng     if(SGN (a)! =0) L.a=p (-C/A,0); -     ElseL.a=p (0,-c/b); the     returnl; + } A voidGet_line () { the      for(intI=2; i<=n;++i) +L[++cnt]=get_line (s[1],s[2],s[i],s[i+1]); -      for(intI=1; i<=n;++i) { $L[++cnt].a=S[i]; $l[cnt].b=s[i+1]-S[i]; -     } -      for(intI=1; i<=cnt;++i) thel[i].ang=atan2 (l[i].b.y,l[i].b.x); - }Wuyi P Inter (L a,l b) { theP p=b.a-a.a; -     Doublet= (p*b.b)/(a.b*b.b); Wu P ans; -ans.x=a.a.x+a.b.x*T; Aboutans.y=a.a.y+a.b.y*T; $     returnans; - } - BOOLJud (L a,l b,l c) { -P p=Inter (A, b); A     return(P-C.A) *c.b>0; + } the voidGet_point () { -Sort (L +1, l+cnt+1); tot=1; $      for(intI=2; i<=cnt;++i) the         if(SGN (l[i].ang-l[i-1].ang)! =0) thel[++tot]=L[i]; thecnt=tot;tot=0, h=1; theq[++r]=l[1];q[++r]=l[2]; -      for(intI=3; i<=cnt;++i) { in         if(SGN (q[r].b*q[r-1].B) = =0)return; the         if(SGN (q[h].b*q[h+1].B) = =0)return; the          while(H<r&&jud (q[r-1],q[r],l[i]) r--; About          while(H<r&&jud (q[h+1],q[h],l[i]) h++; theq[++r]=L[i]; the     } the      while(H<r&&jud (q[r-1],Q[R],Q[H]) r--; +      while(H<r&&jud (q[h+1],Q[H],Q[R]) h++; -q[r+1]=Q[h]; the      for(inti=h;i<=r;++i)BayiP[++tot]=inter (q[i],q[i+1]); thep[++tot]=p[1]; the } - Doubleget_s (P a[],intCNT) { -     Doubleans=0; the     if(cnt<3)return 0; the      for(intI=1; i<cnt;++i) { theans+=a[i]*a[i+1]; the     } -Ans=fabs (ans/2); the     returnans; the } the voidinit () {94scanf"%d",&n); the      for(intI=1; i<=n;++i) { the         intX,Y;SCANF ("%d%d",&x,&y); thes[i].x=x;s[i].y=y;98     } Abouts[n+1]=s[1]; - }101 voidWork () {102 get_line ();103 get_point ();104s1=get_s (s,n+1); theS2=get_s (p,tot);106ans=s2/S1;107printf"%.4LF", ans);108 }109 intMain () { the init ();111 Work (); the     return 0;113}

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Bzoj 4445 [SCOI2015] xiao Convex want to run