1.  /***************
  2.  poj 3335  点序顺时针
  3.  ***************/
  4.  #include <iostream>
  5.  #include <cmath>
  6.  #include <algorithm>
  7.  using namespace std;
  8.  const double eps = 1e-;
  9.  const double maxn = 0x7f7f7f7f;
  10.  int dcmp(double x){
  11.      if(fabs(x)<eps)
  12.          return ;
  13.      else
  14.          return x<?-:;
  15.  }
  16.  struct point {
  17.      double x,y;
  18.      point (double x=,double y =):x(x),y(y){}
  19.  };
  20.  point p[];
  21.  typedef point Vector;
  22.  
  23.  struct polygon{
  24.      point p[];
  25.      int Size;
  26.  };
  27.  
  28.  struct line{
  29.      point fir,sec;
  30.      line(point a = point(),point b = point()){
  31.          fir = a;
  32.          sec = b;
  33.      }
  34.  };
  35.  
  36.  Vector operator -(point a,point b){
  37.      return Vector(a.x-b.x,a.y-b.y);
  38.  }
  39.  
  40.  Vector operator *(Vector a,double p){
  41.      return Vector (a.x*p,a.y*p);
  42.  }
  43.  Vector operator + (Vector a,Vector b){
  44.      return Vector (a.x+b.x,a.y+b.y);
  45.  }
  46.  
  47.  double cross(Vector a,Vector b){
  48.      return a.x*b.y-a.y*b.x;
  49.  }
  50.  
  51.  double dot(Vector a,Vector b){
  52.      return a.x*b.x+a.y*b.y;
  53.  }
  54.  
  55.  point getLineIntersection(point p,Vector v,point q,Vector w){
  56.      Vector u = p-q;
  57.      double t = cross(w,u)/cross(v,w);
  58.      return p+v*t;
  59.  }
  60.  
  61.  bool onsegment(point p,point a1,point a2){
  62.      return dcmp(cross(a1-p,a2-p))==&&dcmp(dot(a1-p,a2-p))<;
  63.  }
  64.  
  65.  polygon cutploygon(polygon poly,line ln){
  66.      polygon newploy;
  67.      int m=;
  68.      int n = poly.Size;
  69.      point a = ln.fir,b = ln.sec;
  70.      for(int i=;i<n;i++){
  71.          point c = poly.p[i];
  72.          point d = poly.p[(i+)%n];
  73.          double cc = cross(b-a,c-a);
  74.          double dd = cross(b-a,d-a);
  75.          if(cc>=)
  76.              newploy.p[m++] = c;
  77.          if(cc*dd<)
  78.              newploy.p[m++] = getLineIntersection(a,b-a,c,d-c);
  79.      }
  80.      newploy.Size = m;
  81.      return newploy;
  82.  }
  83.  
  84.  int main()
  85.  {
  86.      int t;
  87.      cin>>t;
  88.      int n;
  89.      while(t--){
  90.          cin>>n;
  91.          for(int i=;i<n;i++)
  92.              cin>>p[i].x>>p[i].y;
  93.          polygon poly;
  94.          poly.Size = ;
  95.          poly.p[].x = -maxn;
  96.          poly.p[].y = -maxn;
  97.          poly.p[].x = maxn;
  98.          poly.p[].y = -maxn;
  99.          poly.p[].x = maxn;
  100.          poly.p[].y = maxn;
  101.          poly.p[].x = -maxn;
  102.          poly.p[].y = maxn;
  103.          bool flag = true;
  104.          for(int i=;i<=n;i++){
  105.              line ln;
  106.              ln.fir = p[i%n];
  107.              ln.sec = p[i-];
  108.              poly = cutploygon(poly,ln);
  109.              if(poly.Size==){
  110.                  flag = false;
  111.                  break;
  112.              }
  113.          }
  114.          if(!flag)
  115.              cout<<"NO"<<endl;
  116.          else
  117.              cout<<"YES"<<endl;
  118.      }
  119.      return ;
  120.  }
  121.  
  122.  /****************************************/
  123.  poj   点序逆时针
  124.  /****************************************/
  125.  
  126.  #include <iostream>
  127.  #include <cmath>
  128.  #include <algorithm>
  129.  using namespace std;
  130.  const double eps = 1e-;
  131.  const double maxn = 0x7f7f7f7f;
  132.  int dcmp(double x){
  133.      if(fabs(x)<eps)
  134.          return ;
  135.      else
  136.          return x<?-:;
  137.  }
  138.  struct point {
  139.      double x,y;
  140.      point (double x=,double y =):x(x),y(y){}
  141.  };
  142.  point p[];
  143.  typedef point Vector;
  144.  
  145.  struct polygon{
  146.      point p[];
  147.      int Size;
  148.  };
  149.  
  150.  struct line{
  151.      point fir,sec;
  152.      line(point a = point(),point b = point()){
  153.          fir = a;
  154.          sec = b;
  155.      }
  156.  };
  157.  
  158.  Vector operator -(point a,point b){
  159.      return Vector(a.x-b.x,a.y-b.y);
  160.  }
  161.  
  162.  Vector operator *(Vector a,double p){
  163.      return Vector (a.x*p,a.y*p);
  164.  }
  165.  Vector operator + (Vector a,Vector b){
  166.      return Vector (a.x+b.x,a.y+b.y);
  167.  }
  168.  
  169.  double cross(Vector a,Vector b){
  170.      return a.x*b.y-a.y*b.x;
  171.  }
  172.  
  173.  double dot(Vector a,Vector b){
  174.      return a.x*b.x+a.y*b.y;
  175.  }
  176.  
  177.  point getLineIntersection(point p,Vector v,point q,Vector w){
  178.      Vector u = p-q;
  179.      double t = cross(w,u)/cross(v,w);
  180.      return p+v*t;
  181.  }
  182.  
  183.  bool onsegment(point p,point a1,point a2){
  184.      return dcmp(cross(a1-p,a2-p))==&&dcmp(dot(a1-p,a2-p))<;
  185.  }
  186.  
  187.  polygon cutploygon(polygon poly,line ln){
  188.      polygon newploy;
  189.      int m=;
  190.      int n = poly.Size;
  191.      point a = ln.fir,b = ln.sec;
  192.      for(int i=;i<n;i++){
  193.          point c = poly.p[i];
  194.          point d = poly.p[(i+)%n];
  195.          double cc = cross(b-a,c-a);
  196.          double dd = cross(b-a,d-a);
  197.          if(cc>=)
  198.              newploy.p[m++] = c;
  199.          if(cc*dd<)
  200.              newploy.p[m++] = getLineIntersection(a,b-a,c,d-c);
  201.      }
  202.      newploy.Size = m;
  203.      return newploy;
  204.  }
  205.  
  206.  int main()
  207.  {
  208.      int n;
  209.      while(cin>>n&&n){
  210.          for(int i=;i<n;i++)
  211.              cin>>p[i].x>>p[i].y;
  212.          polygon poly;
  213.          poly.Size = ;
  214.          poly.p[].x = -maxn;
  215.          poly.p[].y = -maxn;
  216.          poly.p[].x = maxn;
  217.          poly.p[].y = -maxn;
  218.          poly.p[].x = maxn;
  219.          poly.p[].y = maxn;
  220.          poly.p[].x = -maxn;
  221.          poly.p[].y = maxn;
  222.          bool flag = true;
  223.          for(int i=;i<n;i++){
  224.              line ln;
  225.              ln.fir = p[i%n];
  226.              ln.sec = p[(i+)%n];
  227.              poly = cutploygon(poly,ln);
  228.              if(poly.Size==){
  229.                  flag = false;
  230.                  break;
  231.              }
  232.          }
  233.          if(!flag)
  234.              cout<<""<<endl;
  235.          else
  236.              cout<<""<<endl;
  237.      }
  238.      return ;
  239.  }
  240.  
  241.  /*************************************/
  242.  poj    点序顺时针
  243.  /*************************************/
  244.  #include <iostream>
  245.  #include <cmath>
  246.  #include <algorithm>
  247.  using namespace std;
  248.  const double eps = 1e-;
  249.  const double maxn = 0x7f7f7f7f;
  250.  int dcmp(double x){
  251.      if(fabs(x)<eps)
  252.          return ;
  253.      else
  254.          return x<?-:;
  255.  }
  256.  struct point {
  257.      double x,y;
  258.      point (double x=,double y =):x(x),y(y){}
  259.  };
  260.  point p[];
  261.  typedef point Vector;
  262.  
  263.  struct polygon{
  264.      point p[];
  265.      int Size;
  266.  };
  267.  
  268.  struct line{
  269.      point fir,sec;
  270.      line(point a = point(),point b = point()){
  271.          fir = a;
  272.          sec = b;
  273.      }
  274.  };
  275.  
  276.  Vector operator -(point a,point b){
  277.      return Vector(a.x-b.x,a.y-b.y);
  278.  }
  279.  
  280.  Vector operator *(Vector a,double p){
  281.      return Vector (a.x*p,a.y*p);
  282.  }
  283.  Vector operator + (Vector a,Vector b){
  284.      return Vector (a.x+b.x,a.y+b.y);
  285.  }
  286.  
  287.  double cross(Vector a,Vector b){
  288.      return a.x*b.y-a.y*b.x;
  289.  }
  290.  
  291.  double dot(Vector a,Vector b){
  292.      return a.x*b.x+a.y*b.y;
  293.  }
  294.  
  295.  point getLineIntersection(point p,Vector v,point q,Vector w){
  296.      Vector u = p-q;
  297.      double t = cross(w,u)/cross(v,w);
  298.      return p+v*t;
  299.  }
  300.  
  301.  bool onsegment(point p,point a1,point a2){
  302.      return dcmp(cross(a1-p,a2-p))==&&dcmp(dot(a1-p,a2-p))<;
  303.  }
  304.  
  305.  polygon cutploygon(polygon poly,line ln){
  306.      polygon newploy;
  307.      int m=;
  308.      int n = poly.Size;
  309.      point a = ln.fir,b = ln.sec;
  310.      for(int i=;i<n;i++){
  311.          point c = poly.p[i];
  312.          point d = poly.p[(i+)%n];
  313.          double cc = cross(b-a,c-a);
  314.          double dd = cross(b-a,d-a);
  315.          if(cc>=)
  316.              newploy.p[m++] = c;
  317.          if(cc*dd<)
  318.              newploy.p[m++] = getLineIntersection(a,b-a,c,d-c);
  319.      }
  320.      newploy.Size = m;
  321.      return newploy;
  322.  }
  323.  
  324.  int main()
  325.  {
  326.      int n;
  327.      int cnt =;
  328.      while(cin>>n&&n){
  329.          for(int i=;i<n;i++)
  330.              cin>>p[i].x>>p[i].y;
  331.          polygon poly;
  332.          poly.Size = ;
  333.          poly.p[].x = -maxn;
  334.          poly.p[].y = -maxn;
  335.          poly.p[].x = maxn;
  336.          poly.p[].y = -maxn;
  337.          poly.p[].x = maxn;
  338.          poly.p[].y = maxn;
  339.          poly.p[].x = -maxn;
  340.          poly.p[].y = maxn;
  341.          bool flag = true;
  342.          for(int i=;i<=n;i++){
  343.              line ln;
  344.              ln.fir = p[i%n];
  345.              ln.sec = p[i-];
  346.              poly = cutploygon(poly,ln);
  347.              if(poly.Size==){
  348.                  flag = false;
  349.                  break;
  350.              }
  351.          }
  352.          //cout<<poly.Size<<endl;
  353.          cout<<"Floor #"<<cnt++<<endl;
  354.          if(!flag)
  355.              cout<<"Surveillance is impossible."<<endl;
  356.          else
  357.              cout<<"Surveillance is possible."<<endl;
  358.          cout<<endl;
  359.      }
  360.      return ;
  361.  }
  362.  
  363.  /**********************************
  364.  poj 1279  点序顺时针
  365.  **********************************/
  366.  #include <iostream>
  367.  #include <cmath>
  368.  #include <algorithm>
  369.  #include <cstdio>
  370.  using namespace std;
  371.  const double eps = 1e-;
  372.  const double maxn = 0x7f7f7f7f;
  373.  int dcmp(double x){
  374.      if(fabs(x)<eps)
  375.          return ;
  376.      else
  377.          return x<?-:;
  378.  }
  379.  struct point {
  380.      double x,y;
  381.      point (double x=,double y =):x(x),y(y){}
  382.  };
  383.  point p[];
  384.  typedef point Vector;
  385.  
  386.  struct polygon{
  387.      point p[];
  388.      int Size;
  389.  };
  390.  
  391.  struct line{
  392.      point fir,sec;
  393.      line(point a = point(),point b = point()){
  394.          fir = a;
  395.          sec = b;
  396.      }
  397.  };
  398.  
  399.  Vector operator -(point a,point b){
  400.      return Vector(a.x-b.x,a.y-b.y);
  401.  }
  402.  
  403.  Vector operator *(Vector a,double p){
  404.      return Vector (a.x*p,a.y*p);
  405.  }
  406.  Vector operator + (Vector a,Vector b){
  407.      return Vector (a.x+b.x,a.y+b.y);
  408.  }
  409.  
  410.  double cross(Vector a,Vector b){
  411.      return a.x*b.y-a.y*b.x;
  412.  }
  413.  
  414.  double dot(Vector a,Vector b){
  415.      return a.x*b.x+a.y*b.y;
  416.  }
  417.  
  418.  point getLineIntersection(point p,Vector v,point q,Vector w){
  419.      Vector u = p-q;
  420.      double t = cross(w,u)/cross(v,w);
  421.      return p+v*t;
  422.  }
  423.  
  424.  bool onsegment(point p,point a1,point a2){
  425.      return dcmp(cross(a1-p,a2-p))==&&dcmp(dot(a1-p,a2-p))<;
  426.  }
  427.  
  428.  polygon cutploygon(polygon poly,line ln){
  429.      polygon newploy;
  430.      int m=;
  431.      int n = poly.Size;
  432.      point a = ln.fir,b = ln.sec;
  433.      for(int i=;i<n;i++){
  434.          point c = poly.p[i];
  435.          point d = poly.p[(i+)%n];
  436.          double cc = cross(b-a,c-a);
  437.          double dd = cross(b-a,d-a);
  438.          if(cc>=)
  439.              newploy.p[m++] = c;
  440.          if(cc*dd<)
  441.              newploy.p[m++] = getLineIntersection(a,b-a,c,d-c);
  442.      }
  443.      newploy.Size = m;
  444.      return newploy;
  445.  }
  446.  
  447.  double polyArea(point *p,int n){
  448.      double area =;
  449.      for(int i=;i<n-;i++){
  450.          area += cross(p[i]-p[],p[i+]-p[]);
  451.      }
  452.      return area/;
  453.  }
  454.  
  455.  int main()
  456.  {
  457.      int t;
  458.      cin>>t;
  459.      int n;
  460.      while(t--){
  461.          cin>>n;
  462.          for(int i=;i<n;i++)
  463.              cin>>p[i].x>>p[i].y;
  464.          polygon poly;
  465.          poly.Size = ;
  466.          poly.p[].x = -maxn;
  467.          poly.p[].y = -maxn;
  468.          poly.p[].x = maxn;
  469.          poly.p[].y = -maxn;
  470.          poly.p[].x = maxn;
  471.          poly.p[].y = maxn;
  472.          poly.p[].x = -maxn;
  473.          poly.p[].y = maxn;
  474.          bool flag = true;
  475.          for(int i=;i<=n;i++){
  476.              line ln;
  477.              ln.fir = p[i%n];
  478.              ln.sec = p[i-];
  479.              poly = cutploygon(poly,ln);
  480.              if(poly.Size==){
  481.                  flag = false;
  482.                  break;
  483.              }
  484.          }
  485.          double res;
  486.          if(!flag)
  487.              res =;
  488.          else{
  489.              res = polyArea(poly.p,poly.Size);
  490.          }
  491.          printf("%.2lf\n",res);
  492.      }
  493.      return ;
  494.  }

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