ACM：凸包问题

来源：互联网发布：wifi信号与网络延时编辑：程序博客网时间：2024/05/23 17:57
#include <stdio.h>#include <math.h>#include <stdlib.h>typedef struct{    double x;    double y;}POINT;POINT result[102];                          //保存凸包上的点POINT a[102];                               int n,top;double Distance(POINT p1,POINT p2)          //两点间的距离{    return sqrt((p1.x-p2.x)*(p1.x-p2.x)+(p1.y-p2.y)*(p1.y-p2.y));}double Multiply(POINT p1,POINT p2,POINT p3) //叉积{      return ((p2.x-p1.x)*(p3.y-p1.y)-(p2.y-p1.y)*(p3.x-p1.x)); }int Compare(const void *p1,const void *p2){    POINT *p3,*p4;    double m;    p3=(POINT *)p1;     p4=(POINT *)p2;     m=Multiply(a[0],*p3,*p4) ;    if(m<0) return 1;    else if(m==0&&(Distance(a[0],*p3)<Distance(a[0],*p4)))        return 1;    else return -1;}void Tubao(){   int i;   result[0].x=a[0].x;   result[0].y=a[0].y;   result[1].x=a[1].x;   result[1].y=a[1].y;   result[2].x=a[2].x;   result[2].y=a[2].y;   top=2;   for(i=3;i<=n;i++)   {       while(Multiply(result[top-1],result[top],a[i])<=0 && top>2)            top--;       result[top+1].x=a[i].x;       result[top+1].y=a[i].y;       top++;   }}int main(){   int i,p;   double px,py,len,temp;   while(scanf("%d",&n)!=EOF,n)   {       for(i=0;i<n;i++)           scanf("%lf%lf",&a[i].x,&a[i].y);       if(n==1)       {           printf("0.00\n");           continue;       }       else if(n==2)       {           printf("%.2lf\n",Distance(a[0],a[1]));           continue;       }       py=-1;       for(i=0;i<n;i++)       {           if(py==-1 || a[i].y<py)           {               px=a[i].x;               py=a[i].y;               p=i;           }           else if(a[i].y==py && a[i].x<px)           {               px=a[i].x;               py=a[i].y;               p=i;           }       }       //swap(a[0],a[p])       temp=a[0].x;       a[0].x=a[p].x;       a[p].x=temp;       temp=a[0].y;       a[0].y=a[p].y;       a[p].y=temp;       qsort(&a[1],n-1,sizeof(double)*2,Compare);       a[n].x=a[0].x;       a[n].y=a[0].y;       Tubao();       len=0.0;       for(i=0;i<top;i++)           len=len+Distance(result[i],result[i+1]);       printf("%.2lf\n",len);   }   return 0;}
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