POJ 3348

水题。不过，题意。。呵呵了。。

围一个凸包，求出面积，然后除以50就可以了。

+ View Code?

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68

#include <iostream> #include <cstdio> #include <algorithm> #include <cmath>   using namespace std; const int MAXN=10500; struct point {     int x,y; }p[MAXN];   int n; int ans[MAXN],st[MAXN]; int stop,cnt;   bool cmp(point A,point B){     if(A.y<B.y) return true;     else if(A.y==B.y){         if(A.x<B.x) return true;     }     return false; }   bool multi(point a, point b, point c){     return (a.x-c.x)*(b.y-c.y)-(a.y-c.y)*(b.x-c.x)>0; }   void slove(){     stop=cnt=0;     st[stop++]=0; st[stop++]=1;     for(int i=2;i<n;i++){         while(stop>1&&multi(p[i],p[st[stop-1]],p[st[stop-2]])) stop--;         st[stop++]=i;     }     for(int i=0;i<stop;i++)     ans[cnt++]=st[i];     stop=0;     st[stop++]=n-1; st[stop++]=n-2;     for(int i=n-3;i>=0;i--){         while(stop>1&&multi(p[i],p[st[stop-1]],p[st[stop-2]])) stop--;         st[stop++]=i;     }     for(int i=1;i<stop;i++){         ans[cnt++]=st[i];     } }   int cross(point a,point b,point c){     return (a.x-c.x)*(b.y-c.y)-(a.y-c.y)*(b.x-c.x); }   int main(){     while(scanf("%d",&n)!=EOF){         for(int i=0;i<n;i++)         scanf("%d%d",&p[i].x,&p[i].y);         sort(p,p+n,cmp);         slove();         double anst=0;     //  cout<<cnt<<endl;         for(int i=1;i<cnt-2;i++){             anst+=cross(p[ans[i]],p[ans[i+1]],p[ans[0]]);         }         anst=fabs(anst)/2;     //  cout<<anst<<endl;         printf("%d\n",int(anst/50));     }     return 0; }