hdu 2215 (最小覆寫圓)(目前WA)

(思路明顯錯了)

最小覆寫圓必定是某三個頂點的外接圓。

先求凸包再枚舉。

// hdu 2215.cpp : Defines the entry point for the console application.

//

#include "stdafx.h"

#include "math.h"

#include <iostream>

using namespace std;

#define ABS_N(x) ((x)<0?-(x):(x))

int N,stack_top;

struct Node

{

int x,y;

}m_stack[1005],position[1005];

inline int CrossMutiply(Node p1,Node p2,Node p3)

{

return (p2.x-p1.x)*(p3.y-p1.y)-(p2.y-p1.y)*(p3.x-p1.x);

}

inline int Distance(Node p1,Node p2)

{

return (p1.x-p2.x)*(p1.x-p2.x)+(p1.y-p2.y)*(p1.y-p2.y);

}

int CMP(const void* a,const void* b)

{

Node *p1=(Node*)a,*p2=(Node*)b;

int m=CrossMutiply(position[0],*p1,*p2);

if(m==0) return Distance(position[0],*p1)-Distance(position[0],*p2);

else return -m;

}

void Convex()

{

int swap=0;

for(int i=1;i<N;i++)

{

if((position[i].y<position[swap].y)||(position[i].y==position[swap].y&&position[i].x<position[swap].x))

swap=i;

}

Node temp=position[swap];

position[swap]=position[0];

position[0]=temp;

qsort(position+1,N-1,sizeof(position[0]),CMP);

m_stack[0]=position[0];

m_stack[1]=position[1];

stack_top=1;

for(int i=2;i<N;i++)

{

while(stack_top>=1&&CrossMutiply(m_stack[stack_top-1],m_stack[stack_top],position[i])<=0)

stack_top--;

m_stack[++stack_top]=position[i];

}

}

inline double Diameter(Node p1,Node p2,Node p3)

{

double temp=sqrt((double)Distance(p2,p3));

double temp2=CrossMutiply(p1,p2,p3);

temp2=temp2/(sqrt((double)(Distance(p1,p2)*Distance(p1,p3))));

temp=temp/temp2;

return ABS_N(temp);

}

int main()

{

freopen("d://1.txt","r",stdin);

double ans,temp;

while(scanf("%d",&N)&&N)

{

for(int i=0;i<N;i++)

{

scanf("%d%d",&position[i].x,&position[i].y);

}

if(N==1)

{

printf("%.2f/n",0.5);

continue;

}

else if(N==2)

{

printf("%.2f/n",sqrt((double)Distance(position[0],position[1]))/2+0.5);

continue;

}

Convex();

if(stack_top==1)

{

printf("%.2f/n",sqrt((double)Distance(m_stack[0],m_stack[1]))/2+0.5);

continue;

}

ans=0;

for(int i=0;i<stack_top-1;i++)

{

for(int j=i+1;j<stack_top;j++)

{

for(int k=j+1;k<=stack_top;k++)

{

temp=Diameter(m_stack[i],m_stack[j],m_stack[k]);

if(temp>ans) ans=temp;

}

}

}

printf("%.2f/n",ans/2+0.5);

}

return 0;

}