POJ 3348 Cows(凸包面积)

来源：互联网发布：数据库的模型编辑：程序博客网时间：2024/06/05 06:45

题意：求凸包面积/50，取整

#include <iostream>#include <cstdio>#include <cstring>#include <algorithm>#include <cmath>#include <queue>#include <stack>using namespace std;double EPS = 1e-12;struct cpoint{    double x,y;    void get(){scanf("%lf%lf",&x,&y);}};double x_mult(cpoint a,cpoint b,cpoint c){    return (a.x-c.x)*(b.y-c.y)-(a.y-c.y)*(b.x-c.x);}int cmp(cpoint const a,const cpoint b){    return a.y<b.y||(a.y==b.y&&a.x<b.x);}int granham(cpoint p[],int s,cpoint r[]){    int i,len,top = 1;    sort(p,p+s,cmp);    r[0]= p[0],r[1] = p[1];    if(s<3) return s;    for(i=2;i<s;i++)    {        while(top&&x_mult(p[i],r[top],r[top-1])>EPS) top--;        r[++top] = p[i];    }    len = top;r[++top] = p[s-2];    for(i=s-3;i>=0;i--)    {        while(top!=len&&x_mult(p[i],r[top],r[top-1])>EPS) top--;        r[++top] = p[i];    }    return top;}double area(cpoint p[],int s){    double ret=0;    if(s<3) return 0;    for(int i=1;i<s-1;i++)    {        ret+=x_mult(p[i],p[i+1],p[0]);    }ret/=2;    return ret;}cpoint p[10009],ans[10009];int main(){    freopen("in.txt","r",stdin);    int n;    scanf("%d",&n);    for(int i=0;i<n;i++) p[i].get();    int k = granham(p,n,ans);    double a = area(ans,k);    printf("%d\n",int(a/50));    return 0;}