hdu 3934&&poj 2079 （凸包+旋转卡壳+求最大三角形面积）

  1 #include <math.h>
  2 #include <stdio.h>
  3 #include <string.h>
  4 #include <stdlib.h>
  5 #include <iostream>
  6 #include <algorithm>
  7 
  8 using namespace std;
  9 
 10 #define eps 1e-8
 11 #define MAXX 1000010
 12 
 13 typedef struct point
 14 {
 15 
 16     double x;
 17     double y;
 18 }point;
 19 
 20 bool dy(double x,double y){
 21     return x>y+eps; }
 22 bool xy(double x,double y){
 23     return x<y-eps; }
 24 bool dyd(double x,double y){
 25     return x>y-eps; }
 26 bool xyd(double x,double y){
 27     return x<y+eps; }
 28 bool dd(double x,double y){
 29     return fabs(x-y)<eps; }
 30 
 31 double crossProduct(point a,point b,point c)
 32 {
 33     return (c.x-a.x)*(b.y-a.y)-(c.y-a.y)*(b.x-a.x);
 34 }
 35 
 36 double dist(point a,point b)
 37 {
 38 
 39     return sqrt((b.x-a.x)*(b.x-a.x)+(b.y-a.y)*(b.y-a.y));
 40 }
 41 
 42 point c[MAXX];
 43 point stk[MAXX];
 44 int top;
 45 
 46 bool cmp(point a,point b)
 47 {
 48 
 49     double len=crossProduct(c[0],a,b);
 50     if(dd(len,0.0))
 51         return xy(dist(c[0],a),dist(c[0],b));
 52     return xy(len,0.0);
 53 }
 54 
 55 double max(double x,double y)
 56 {
 57 
 58     return xy(x,y) ? y : x;
 59 }
 60 
 61 void Graham(int n)
 62 {
 63 
 64     int tmp=0;
 65     for(int i=1; i<n; i++)
 66     {
 67 
 68         if(xy(c[i].x,c[tmp].x) || dd(c[i].x,c[tmp].x) && xy(c[i].y,c[tmp].y))
 69             tmp=i;
 70     }
 71     swap(c[0],c[tmp]);
 72     sort(c+1,c+n,cmp);
 73     stk[0]=c[0];
 74     stk[1]=c[1];
 75     top=1;
 76     for(int i=2; i<n; i++)
 77     {
 78         while(top>=1 && xyd(crossProduct(stk[top],stk[top-1],c[i]),0.0))
 79             top--;
 80         stk[++top]=c[i];
 81     }
 82 }
 83 
 84 double rotating(int n)
 85 {
 86     int j=1,k=2;
 87     double ans=0.0;
 88     stk[n]=stk[0];
 89     for(int i=0; i<n; i++)
 90     {
 91         while(dy(fabs(crossProduct(stk[(k+1)%n],stk[i],stk[j])),fabs(crossProduct(stk[k],stk[i],stk[j]))))
 92             k=(k+1)%n;
 93         while(dy(fabs(crossProduct(stk[k],stk[i],stk[(j+1)%n])),fabs(crossProduct(stk[k],stk[i],stk[j]))))
 94             j=(j+1)%n;
 95         ans=max(ans,fabs(crossProduct(stk[k],stk[i],stk[j])));
 96     }
 97     return ans*0.5;
 98 }
 99 
100 int main()
101 {
102 
103     int i,j,n;
104     while(scanf("%d",&n)!=EOF&&n != -1)
105     {
106 
107         for(i=0; i<n; i++)
108             scanf("%lf%lf",&c[i].x,&c[i].y);
109         Graham(n);//printf("%d**",top);
110         double ans=rotating(top+1);
111         printf("%.2lf\n",ans);
112     }
113     return 0;
114 }
115