hdu 2215 (最小覆盖圆)(目前WA)

(思路明显错了)

最小覆盖圆必定是某三个顶点的外接圆。

先求凸包再枚举。

 

// 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;}