HDUOJ-------Naive and Silly Muggles
Naive and Silly Muggles
Time Limit: 2000/1000 MS (Java/Others) Memory Limit: 32768/32768 K (Java/Others) Total Submission(s): 61 Accepted Submission(s): 39
通俗算法
定义:设平面上的三点A(x1,y1),B(x2,y2),C(x3,y3),定义
S(A,B,C) = (x1-x3)*(y2-y3) - (y1-y3)*(x2-x3) 已知三角形的三个顶点为A(x1,y1),B(x2,y2),C(x3,y3),则该三角形的外心为:
S((x1*x1+y1*y1, y1), (x2*x2+y2*y2, y2), (x3*x3+y3*y3, y3))
x0 = -----------------------------------------------------------
*S(A,B,C) S((x1,x1*x1+y1*y1), (x2, x2*x2+y2*y2), (x3, x3*x3+y3*y3))
y0 = -----------------------------------------------------------
*S(A,B,C)
代码形式:
//求外接圆的圆心
double S(double x1,double y1,double x2,double y2,double x3,double y3){
return ((x1-x3)*(y2-y3) - (y1-y3)*(x2-x3) );
} double getx(double x1,double y1,double x2,double y2,double x3,double y3){
return (S(x1*x1+y1*y1,y1, x2*x2+y2*y2, y2,x3*x3+y3*y3,y3)/(*S(x1,y1,x2,y2,x3,y3)) );
} double gety(double x1,double y1,double x2,double y2,double x3,double y3){
return (S(x1, x1*x1+y1*y1, x2, x2*x2+y2*y2, x3, x3*x3+y3*y3) / (*S(x1,y1,x2,y2,x3,y3)));
}
#include<iostream>
#include<cstdio>
#include<cstring>
#include<cmath>
using namespace std;
bool isline(double *a,double *b,double *c)
{
if(fabs((b[]-a[])*(c[]-a[])-(c[]-a[])*(b[]-a[]))<1e-)
return ;
else
return ;
}
//求外接圆的圆心
double S(double x1,double y1,double x2,double y2,double x3,double y3){
return ((x1-x3)*(y2-y3) - (y1-y3)*(x2-x3) );
} double getx(double x1,double y1,double x2,double y2,double x3,double y3){
return (S(x1*x1+y1*y1,y1, x2*x2+y2*y2, y2,x3*x3+y3*y3,y3)/(*S(x1,y1,x2,y2,x3,y3)) );
} double gety(double x1,double y1,double x2,double y2,double x3,double y3){
return (S(x1, x1*x1+y1*y1, x2, x2*x2+y2*y2, x3, x3*x3+y3*y3) / (*S(x1,y1,x2,y2,x3,y3)));
}
//求两条边的夹角
bool iftrue(double *a,double *b,double *c )
{
return (a[]-b[])*(c[]-b[])+(a[]-b[])*(c[]-b[])>?:; //不是锐角时yes
}
//求两点间的距离
double distan(double *a,double *b)
{
return sqrt((a[]-b[])*(a[]-b[])+(a[]-b[])*(a[]-b[]))/2.0;
} int main()
{
int t,count,i;
double po[][],r,save[][],x,y;
scanf("%d",&t);
for(count=;count<=t;count++)
{
for(i=;i<;i++)
{
scanf("%lf%lf",&po[i][],&po[i][]);
if(i==||save[][]*save[][]+save[][]*save[][]<po[i][]*po[i][]+po[i][]*po[i][])
save[][]=po[i][],save[][]=po[i][];
if(i==||save[][]*save[][]+save[][]*save[][]>po[i][]*po[i][]+po[i][]*po[i][])
save[][]=po[i][],save[][]=po[i][];
}
if(isline(po[],po[],po[]))
{
r=sqrt((save[][]-save[][])*(save[][]-save[][])+(save[][]-save[][])*(save[][]-save[][]))/2.0;
x=(save[][]+save[][])/2.0;
y=(save[][]+save[][])/2.0;
}
else
{
bool judge[];
judge[]=iftrue(po[],po[],po[]);
judge[]=iftrue(po[],po[],po[]);
judge[]=iftrue(po[],po[],po[]);
if(judge[]||judge[]||judge[])
{
if(judge[])
{
x=(po[][]+po[][])/2.0;
y=(po[][]+po[][])/2.0;
r=distan(po[],po[]);
}
else if(judge[])
{
x=(po[][]+po[][])/2.0;
y=(po[][]+po[][])/2.0;
r=distan(po[],po[]);
}
else if(judge[])
{
x=(po[][]+po[][])/2.0;
y=(po[][]+po[][])/2.0;
r=distan(po[],po[]);
}
}
else
{
//当为锐角时,求其外接圆,否者不求
x=getx(po[][],po[][],po[][],po[][],po[][],po[][]);
y=gety(po[][],po[][],po[][],po[][],po[][],po[][]);
r=sqrt((po[][]-x)*(po[][]-x)+(po[][]-y)*(po[][]-y));
}
}
double temp=sqrt((po[][]-x)*(po[][]-x)+(po[][]-y)*(po[][]-y));
if(r>temp-1e-)
printf("Case #%d: Danger\n",count);
else
printf("Case #%d: Safe\n",count);
}
return ;
}
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